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Disorders of pigmentation.pptx

This document discusses disorders of pigmentation. It begins with an introduction to melanocytes and melanin production. It then describes disorders characterized by hypopigmentation, including vitiligo, oculocutaneous albinism, tuberous sclerosis ash leaf spots, piebaldism, pityriasis alba, idiopathic guttate hypomelanosis, and postinflammatory hypopigmentation. The document concludes by discussing some disorders characterized by hyperpigmentation such as melasma.

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Disorders of pigmentation Presenter – Dr. Eyasu (R1) Moderator- Dr. Hadas (Pathologist) 1
Outline • Introduction • Disorders characterized by hypopigmentation • Disorders characterized by hyperpigmentation • References 2
Introduction • Melanocytes are found along the dermal-epidermal junction as well as within hair follicles. • Responsible for the production and secretion of melanin pigment. • Characterized by small, dark, ovoid nuclei and scant, clear cytoplasm. • They number from one per 10 to one per five basal keratinocytes, with higher concentrations on the face and genitalia. • Pigment is not normally visible in their cytoplasms because it is rapidly secreted and taken up by basal keratinocytes, where it is stored and gradually broken down. • Although the amount of melanin produced and stored varies between darker and lighter skinned individuals, the number of melanocytes does not. 3 Melanocytes
Introduction… • The pigmentary system involves a complex set of reactions with numerous potential sites for dysfunction. • Melanin is produced in melanosomes in the cytoplasm of melanocytes by the action of tyrosinase on tyrosine. • The melanin synthesized in any one melanocyte is then transferred to an average of 36 keratinocytes. 1) Through the phagocytosis of the melanin-laden dendritic tips of the melanocytes. 2) Exocytosis of melanocores (polymerized melanin) followed by release into the extracellular space and ingestion by adjacent keratinocytes. • Any inflammatory process involving the epidermal basilar layer that can disrupt this transfer of melanin as well as specific enzyme defects and destruction of melanocytes may result in hypopigmentation. • The pathogenesis of hyperpigmentation is not as well understood. • Prominent pigment incontinence and increase in size or melanization of the melanosomes are possible mechanisms. 4
Introduction… • This seminar deals with the various disorders of cutaneous pigmentation, excluding those entities in which there is an obvious lentiginous proliferation of melanocytes and tumors of the nevus cell–melanocyte system. 5
1. Disorders Characterized By Hypopigmentation • Categories on the basis of their presumed pathogenesis. 1) Abnormal migration/differentiation of melanoblasts: piebaldism, Waardenburg’s and Woolf ’s syndromes 2) Destruction of melanocytes: vitiligo, chemical leukoderma 3) Reduced tyrosinase activity: oculocutaneous albinism type 1A 4) Abnormal structure of melanosomes: “ash leaf spots”, Chédiak–Higashi syndrome, progressive macular hypomelanosis 5) Reduced melanization and/or numbers of melanosomes: albinism, Griscelli syndrome, idiopathic guttate hypomelanosis, hypomelanosis of Ito, “ash leaf spots,” pityriasis versicolor, nevus depigmentosus 6) Reduced transfer to keratinocytes: nevus depigmentosus, pityriasis alba, postinflammatory leukoderma, pityriasis versicolor, Chédiak–Higashi syndrome 7) Abnormal vasculature: nevus anemicus 6
1.1. Vitiligo • A common acquired disease of unknown etiology characterized by selective loss of melanocytes. • Incidence- between 1% and 2% of the population. • More common in people with dark skin. • The sex incidence is equal, with a peak age between 10 and 30 years (up to 50% of cases). • Between 25% and 40% of patients have a positive family history of the disease • Almost 15% of late-onset cases demonstrate the Koebner phenomenon. • Approximately 20% to 30% of patients have an associated autoimmune and/or endocrine disorder such as Hashimoto’s disease, hyperthyroidism, pernicious anemia, Addison’s disease, type 1 diabetes mellitus, and alopecia areata. • Childhood-onset vitiligo: female predominance, may show eyelid involvement as the initial site, less common mucosal involvement. 7
1.1. Vitiligo… • Results in symmetrical macular areas of leukoderma that progressively enlarge and often become confluent. • There is a predilection for the face, back of the hands, axillae, groins, umbilicus, and genitalia and for the skin overlying bony areas such as the knees and elbows. • Vitiligo has been reported on the anterior neck in Muslim women. • It is thought to be due to the Koebner phenomenon resulting from the wearing of scarves that are tied with metallic or plastic pins in this region. • Sometimes the depigmented area is segmental or dermatomal in distribution (type B); more often, it is more generalized (type A). • Mucous membrane involvement with vitiligo can involve the lips, gingiva and anogenital region. 8
1.1. Vitiligo… • Some drugs and other agents are reported to produce depigmentation resembling vitiligo: chloroquine, imatinib, zidovudine, lamivudine, efavirenz… • Vitiliginous skin is generally resistant to developing dermatitis in response to contact allergens, and it also has the remarkable property of resistance to forming nonmelanoma skin cancers, in contrast to the depigmented skin of albinos. • Vitiligo may be a presenting sign of metastatic melanoma- patients have a better prognosis than those who do not develop vitiligo-like depigmentation . 9
1.1. Vitiligo… • Pathogenesis- three hypotheses • Neurogenic hypothesis - production of a neurochemical mediator by the nerve endings in the skin, leading to inhibition of melanogenesis and destruction of melanocytes. • Self-destruction theory - proposes that melanocytes are destroyed by toxic melanin precursors such as free radicals. Experimental evidence is based on the fact that a number of chemicals induce pigmentary changes indistinguishable from vitiligo. • Autoimmune hypothesis - based on the observation that patients with vitiligo have an associated autoimmune disease in up to between 15– 30% of cases. 10
1.1. Vitiligo… • Histological features • complete absence of melanocytes in association with total loss of epidermal pigmentation. • Biopsies from the periphery of lesions with a clinically inflammatory border show lymphocytes and histiocytes in the papillary dermis. • Some inflammatory cells may also be found at the periphery, even in the absence of a clinically inflamed border. • At the advancing border, the melanocytes may be increased in size with an increased number of dendrites. 11 S-100 protein
1.1. Vitiligo… • Differential diagnosis • Guttate hypomelanosis- clinical presentation and the complete absence of melanocytes in vitiligo, and the persistence of at least some melanocytes in the former. • Post inflammatory hypopigmentation- preservation of melanocytes with only loss of pigment. 12
1.2. Oculocutaneous Albinism • A genetically heterogeneous group of disorders in which there is a generalized decrease or absence of melanin pigment in the eyes, hair, and skin. • At least 10 forms of this condition have been identified, each presumably resulting from a different biochemical block in the synthesis of melanin. • The most common forms are types 1 and 2, which account for 40% and 50%, respectively, of cases worldwide. • Type 1A is due to complete absence of tyrosinase activity in melanocytes whereas in type 1B there is reduced activity of tyrosinase. • Oculocutaneous albinism type 2 is caused by mutations in the gene OCa2. The OCa2 protein is important in the formation of melanosomes and in transport of melanosomal proteins. 13
1.2. Oculocutaneous Albinism… • The clinical manifestations of oculocutaneous albinism depend on the type of biochemical abnormality. • In all types of albinism, the lack of melanin in the developing eye results in hypoplasia of the fovea and abnormal routing of the optic nerves. • As a result, all patients have variable strabismus, nystagmus, and reduced visual acuity. • Affected patients often have an increased risk of skin cancer. • Based on clinical features alone, it is not always possible to separate the different types of oculocutaneous albinism. • The clinical presentation at birth is white hair and skin and blue eyes. 14
1.2. Oculocutaneous Albinism… • Histological features • Reduced or complete absence of melanin in the epidermis and hair follicles, depending on the type of oculocutaneous albinism. • Melanocytes are normal in number and morphology. • Tyrosinase activity is lacking in melanocytes in freshly plucked anagen hair bulbs in type 1A; it is reduced in heterozygotes with this phenotype and variably reduced in some of the other types. • Tyrosinase activity is normal in type 2. 15
1.3. Tuberous Sclerosis: Hypopigmented Macules (“Ash Leaf Spots”) • Tuberous sclerosis is characterized by the triad of epilepsy, mental retardation, and multiple angiofibromas. • In addition, circumscribed macules of hypopigmentation known as “ash leaf spots” can be present at birth on the trunk and lower extremities. • The basic abnormality appears to be an arrest in the maturation of melanosomes. • They vary in diameter from 1 mm to 12 cm. • The more common shapes are oval, polygonal, or ash leaf–like. 16
1.3. Tuberous Sclerosis: Hypopigmented Macules (“Ash Leaf Spots”)… • Histopathology • Numbers of melanocytes are not decreased in the hypopigmented macules, which can be confirmed with melan-A staining. • Epidermal melanin is reduced but not absent. 17
1.4. Piebaldism • A rare congenital disorder inherited in an autosomal dominant manner. • There are nonprogressive, discrete patches of leukoderma. • The central area of the forehead, the anterior trunk, and the mid areas of the extremities are characteristically affected. • The hands, feet, and back are usually spared. • In 90% of cases there is a white forelock in the frontal mid scalp; this may be the only manifestation of the disease. • Café-au-lait spots are a frequent finding. An association with neurofibromatosis type 1 has been documented. 18
1.4. Piebaldism… • Histological features • complete absence of melanocytes • Abnormal melanocytes may be seen in areas of transition between involved and normal skin. • These melanocytes may have spherical melanosomes. • Some clear cells, representing Langerhans cells, are usually present in the epidermis. 19
1.5. Pityriasis Alba • One of the most common localized disorders of hypopigmentation in children. • Young adults may also be affected. • Slightly more common in dark-skinned atopic males. • Ill-defined, slightly scaly patches of hypopigmentation on the face with predilection for the cheeks. • Also seen on the neck and shoulders. 20
1.5. Pityriasis Alba… • Histologically, the changes are often subtle and consist of mild hyperkeratosis, focal parakeratosis, minimal spongiosis, and variable exocytosis of lymphocytes. • This is associated with mild loss of melanin in basal keratinocytes but not in the number of melanocytes. • In the dermis there is mild pigment incontinence and a sparse superficial, perivascular lymphohistiocytic inflammatory cell infiltrate. 21
1.6. Idiopathic Guttate Hypomelanosis • a common leukodermic dermatosis of unknown cause. • Multiple hypochromic macules, 2 to 5 mm in diameter which develop over many years. • Usually found on the sun- exposed extremities of elderly individuals. • Repigmentation does not occur. 22
1.6. Idiopathic Guttate Hypomelanosis… • Variable loss of melanin granules in epidermal keratinocytes. This is sometimes associated with epidermal atrophy and flattening of the rete ridges. • Orthokeratotic hyperkeratosis in a basket-weave pattern has also been documented. • However, complete loss of melanocytes is not a feature. 23
1.6. Idiopathic Guttate Hypomelanosis… • DDx- lichen sclerosus, hypopigmented mycosis fungoides, atrophie blanche, vitiligo, pityriasis versicolor, leprosy, and the hypopigmented lesions seen in tuberous sclerosis. • Most of these entities are easy to exclude histologically except for vitiligo. • In the latter there is complete absence of melanocytes and this can be confirmed with a melanocyte-specific immunostain such as Melan- a, since S-100 also stains Langerhans cells. 24
1.7. Postinflammatory Hypopigmentation • Inflammation of the skin can result in hyperpigmentation or hypopigmentation. • Postinflammatory hypopigmentation is a very common form of hypopigmentation. • The lack of pigment becomes noticeable as the primary lesion fades. • The lesion is usually a macule with indistinct borders and a variable degree of hypopigmentation. 25
1.7. Postinflammatory Hypopigmentation… • Histologically, there is focal reduction in pigmentation in the basal cell layer of the epidermis. • Residual features of the preceding or concurrent inflammatory dermatosis may also be present. • The diagnosis is usually obvious by the patient’s report of a previous inflammatory lesion at the sites of hypopigmentation. • When no such history can be obtained, the differential diagnosis includes halo nevus, pityriasis alba, pityriasis versicolor, and cutaneous infections such as those resulting from Candida spp. or dermatophytes. • Careful histopathologic examination for the presence of nevus cells and microorganisms should aid in distinguishing postinflammatory hypopigmentation from halo nevus and infectious processes, respectively. 26
2. Disorders Characterized By Hyperpigmentation • The following subclassification provides a useful approach to a biopsy from hyperpigmented lesions: 1. Disorders with basal hyperpigmentation: melasma, acquired brachial dyschromatosis, ephelis (freckle), café-au-lait spots, macules of Albright’s syndrome, Laugier–Hunziker syndrome, Peutz–Jeghers syndrome, and Becker’s nevus (melanosis)… 2. Disorders with epidermal changes: Dowling–Degos disease, Kitamura’s disease, and confluent and reticulated papillomatosis of Gougerot–Carteaud… 3. Disorders with striking melanin incontinence: postinflammatory melanosis, prurigo pigmentosa, generalized melanosis in malignant melanoma… 4. Disorders with melanin incontinence and epidermal atrophy or “dyskeratotic” cells: dyskeratosis congenita, frictional melanosis, active fixed drug eruptions, and active prurigo pigmentosa… 27
2.1. Melasma (chloasma) • An acquired, chronic, recurrent lesion that develops in some women, especially those living in areas of intense UV radiation, who are pregnant or taking oral contraceptives. • Its incidence in pregnancy varies from 15% to 50%. • An association has also been documented with cosmetics, phototoxic drugs, isotretinoin, and anticonvulsants. • Melasma also occurs, though less commonly, in men. • There is a marked predilection for the face (forehead and cheeks). • Symmetrical hyperpigmentation characterized by irregular light to dark-brown confluent or speckled macules with sharply demarcated margins involving sun-exposed skin. 28
2.1. Melasma… • Histologically, there is increased melanin in the epidermis, particularly in the basal layers. • Melanin pigment is located in a “cap” overlying the keratinocyte nuclei. • Normal melanocyte numbers in all cases. • However, melanocytes are enlarged and have increased numbers of dendrites. • Mild pigment incontinence is sometimes present, along with a perivascular lymphohistiocytic infiltrate and increased vascularity. • Solar elastosis is more prominent than in normal skin. • Mast cells are also increased in number. 29
2.2. Cafe´-au-lait spots • “coffee-with-milk” • They may be present at birth or develop within the first few years of life. • They are found in approximately 15% of individuals. • They are not increased in patients with tuberous sclerosis. • Multiple café-au-lait spots are a feature of neurofibromatosis (95% of NF1 patients). Axillary freckling is often also present in these cases. • Café-au-lait spots have also been reported in Bloom’s syndrome, Cowden’s disease, Fanconi’s anemia, ring chromosome syndromes, ataxia–telangiectasia, nevoid BCC syndrome, Legius syndrome, and Noonan’s syndrome. • Uniformly pigmented, tan to dark brown macules with well- defined borders that vary in size from small, freckle-like lesions to large patches 20 cm or more in diameter. 30
2.2. Cafe´-au-lait spots… • An increase in melanin pigment deposition within basilar keratinocytes. • The density of melanocytes is normal or only slightly increased. • The increased pigmentation typically spares the adnexal epithelium. • Giant melanin granules (macromelanosomes) can be seen in café-au-lait spots in many patients with neurofibromatosis. • The diagnostic significance of macromelanosomes is diminished by their absence in some children with neurofibromatosis and their presence in normal skin and other pigmented macular lesions. 31
2.2. Cafe´-au-lait spots… • Differential diagnosis • Postinflammatory hyperpigmentation, melasma, melanocytic nevi. • Café au-lait macules have a tendency to grow in proportion to growth of the rest of the body. • They do not change with sun protection or bleaching agents. • Their completely macular appearance may be helpful for the correct diagnosis. • Histologically café-au-lait macules are usually indistinguishable from freckles, melasma, and the melanotic macules of Albright’s syndrome. • They can be differentiated from melanocytic nevi and simple lentigines by their lack of melanocyte proliferation and rete ridge elongation. • Café-au-lait macules differ from lesions of postinflammatory hyperpigmentation by the presence of an inflammatory infiltrate or pigment incontinence in the latter. 32
2.3. Ephelis (Freckle) • Ephelides (freckles) are small, well-defined, pigmented macules 1 to 2 mm in diameter. • Show predilection for the face, arms, and shoulder regions of fair- skinned individuals. • They appear at an early age and may follow an episode of severe sunburn. • Darken easily with sun exposure. 33
2.3. Ephelis (Freckle)… • The epidermis appears normal in structure. • The basal cells in the affected areas are more heavily pigmented with melanin than those in the surrounding skin. • There is usually sharp delimitation of the abnormal areas from the normal. • There are normal numbers of melanocytes. • No elongation of rete ridges and no nests. 34
2.4. Macules Of Albright’s Syndrome • Albright’s syndrome is characterized by the triad of polyostotic fibrous dysplasia, sexual precocity—especially in the female, and pigmented macules. • These macules are large, often unilateral, and related to the side of the bone lesions. • The outline of the macules is very irregular, in contrast to that of café-au-lait spots. • They mainly involve the trunk and proximal lower limbs and less commonly the face and neck. 35
2.4. Macules Of Albright’s Syndrome… • A skin biopsy from a pigmented macular lesion resemble freckles, showing hyperpigmentation of the basal layer. • Giant melanosomes are sometimes seen but are not as frequent as in the café-au-lait spots of neurofibromatosis type I. • In the dermis and subcutaneous tissue, plaque-like osteomas may be seen. 36
2.5. Becker’s Nevus (melanosis) • Is usually found in the region of the shoulder girdle as unilateral, hyperpigmented areas of somewhat thickened skin. • The male-to-female ratio ranges from 4-6 : 1. • It is more common in young people with fair skin. • Occasionally, lesions have been said to follow severe sunburn. • Hypertrichosis may develop after the pigmentation, but is not invariable. • May be associated with connective tissue nevus, accessory scrotum, areolar hypoplasia. 37
2.5. Becker’s Nevus... • The epidermal changes are variable, but usually there is acanthosis and sometimes mild papillomatous hyperplasia. • Elongated rete ridges with pointed or flat tips. • There is variable hyperpigmentation of the basal layer with some melanophages in the dermis. • Melanocyte proliferation is usually mild and not always obvious in routine sections; special studies have shown a quantitative increase. 38
2.6. Postinflammatory Melanosis • Hyperpigmentation may follow a number of inflammatory dermatoses, particularly those involving damage to the basal layer. • Thus, it may follow various disorders that present a lichenoid reaction pattern, such as lichen planus, lichenoid drug eruptions, and fixed drug eruptions. • Specific drugs that may cause postinflammatory and/or increased basal pigmentation include the following: prostaglandin analogs, interferon-α, olanzapine, hydroxyurea, and calcipotriol. 39
2.6. Postinflammatory Melanosis… • There are two major histopathological types of postinflammatory hyperpigmentation: Epidermal- increased basilar epidermal pigmentation, and Dermal- marked pigmentation in the upper dermis and decreased epidermal pigmentation. • More prominent perivascular lymphocytic inflammation is seen in the dermal pigment group. • Basal pigmentation is prominent in photodermatitis. 40
2.7. Laugier-Hunziker Syndrome • An acquired disorder characterized by macular pigmentation of the lips, oral cavity (mainly hard palate and less commonly buccal mucosa, soft palate, and gums) and, less frequently, fingers and palms. • Longitudinal melanonychia is seen in up to 50% of patients. • Genital and conjunctival pigmentation is very rare. • The sex incidence is similar and most patients are Caucasian and middle aged. 41
2.7. Laugier-Hunziker Syndrome… • Histologically, there is hyperpigmentation of basal keratinocytes and pigment incontinence with melanophages in the papillary dermis. • Recently, it has been suggested that there is an increase in the number of basal dendritic melanocytes and the term ‘mucocutaneous lentiginosis of Laugier and hunziker’ has been proposed. 42
References • Weedon’s Skin Pathology, Fifth Edition • McKee's Pathology of the Skin, Fourth Edition • FDP Dermatopathology, Second Edition • Fitzpatrick’s Dermatology, Ninth Edition 43

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Disorders of pigmentation.pptx

  • 1.
    Disorders of pigmentation Presenter– Dr. Eyasu (R1) Moderator- Dr. Hadas (Pathologist) 1
  • 2.
    Outline • Introduction • Disorderscharacterized by hypopigmentation • Disorders characterized by hyperpigmentation • References 2
  • 3.
    Introduction • Melanocytes arefound along the dermal-epidermal junction as well as within hair follicles. • Responsible for the production and secretion of melanin pigment. • Characterized by small, dark, ovoid nuclei and scant, clear cytoplasm. • They number from one per 10 to one per five basal keratinocytes, with higher concentrations on the face and genitalia. • Pigment is not normally visible in their cytoplasms because it is rapidly secreted and taken up by basal keratinocytes, where it is stored and gradually broken down. • Although the amount of melanin produced and stored varies between darker and lighter skinned individuals, the number of melanocytes does not. 3 Melanocytes
  • 4.
    Introduction… • The pigmentarysystem involves a complex set of reactions with numerous potential sites for dysfunction. • Melanin is produced in melanosomes in the cytoplasm of melanocytes by the action of tyrosinase on tyrosine. • The melanin synthesized in any one melanocyte is then transferred to an average of 36 keratinocytes. 1) Through the phagocytosis of the melanin-laden dendritic tips of the melanocytes. 2) Exocytosis of melanocores (polymerized melanin) followed by release into the extracellular space and ingestion by adjacent keratinocytes. • Any inflammatory process involving the epidermal basilar layer that can disrupt this transfer of melanin as well as specific enzyme defects and destruction of melanocytes may result in hypopigmentation. • The pathogenesis of hyperpigmentation is not as well understood. • Prominent pigment incontinence and increase in size or melanization of the melanosomes are possible mechanisms. 4
  • 5.
    Introduction… • This seminardeals with the various disorders of cutaneous pigmentation, excluding those entities in which there is an obvious lentiginous proliferation of melanocytes and tumors of the nevus cell–melanocyte system. 5
  • 6.
    1. Disorders CharacterizedBy Hypopigmentation • Categories on the basis of their presumed pathogenesis. 1) Abnormal migration/differentiation of melanoblasts: piebaldism, Waardenburg’s and Woolf ’s syndromes 2) Destruction of melanocytes: vitiligo, chemical leukoderma 3) Reduced tyrosinase activity: oculocutaneous albinism type 1A 4) Abnormal structure of melanosomes: “ash leaf spots”, Chédiak–Higashi syndrome, progressive macular hypomelanosis 5) Reduced melanization and/or numbers of melanosomes: albinism, Griscelli syndrome, idiopathic guttate hypomelanosis, hypomelanosis of Ito, “ash leaf spots,” pityriasis versicolor, nevus depigmentosus 6) Reduced transfer to keratinocytes: nevus depigmentosus, pityriasis alba, postinflammatory leukoderma, pityriasis versicolor, Chédiak–Higashi syndrome 7) Abnormal vasculature: nevus anemicus 6
  • 7.
    1.1. Vitiligo • Acommon acquired disease of unknown etiology characterized by selective loss of melanocytes. • Incidence- between 1% and 2% of the population. • More common in people with dark skin. • The sex incidence is equal, with a peak age between 10 and 30 years (up to 50% of cases). • Between 25% and 40% of patients have a positive family history of the disease • Almost 15% of late-onset cases demonstrate the Koebner phenomenon. • Approximately 20% to 30% of patients have an associated autoimmune and/or endocrine disorder such as Hashimoto’s disease, hyperthyroidism, pernicious anemia, Addison’s disease, type 1 diabetes mellitus, and alopecia areata. • Childhood-onset vitiligo: female predominance, may show eyelid involvement as the initial site, less common mucosal involvement. 7
  • 8.
    1.1. Vitiligo… • Resultsin symmetrical macular areas of leukoderma that progressively enlarge and often become confluent. • There is a predilection for the face, back of the hands, axillae, groins, umbilicus, and genitalia and for the skin overlying bony areas such as the knees and elbows. • Vitiligo has been reported on the anterior neck in Muslim women. • It is thought to be due to the Koebner phenomenon resulting from the wearing of scarves that are tied with metallic or plastic pins in this region. • Sometimes the depigmented area is segmental or dermatomal in distribution (type B); more often, it is more generalized (type A). • Mucous membrane involvement with vitiligo can involve the lips, gingiva and anogenital region. 8
  • 9.
    1.1. Vitiligo… • Somedrugs and other agents are reported to produce depigmentation resembling vitiligo: chloroquine, imatinib, zidovudine, lamivudine, efavirenz… • Vitiliginous skin is generally resistant to developing dermatitis in response to contact allergens, and it also has the remarkable property of resistance to forming nonmelanoma skin cancers, in contrast to the depigmented skin of albinos. • Vitiligo may be a presenting sign of metastatic melanoma- patients have a better prognosis than those who do not develop vitiligo-like depigmentation . 9
  • 10.
    1.1. Vitiligo… • Pathogenesis-three hypotheses • Neurogenic hypothesis - production of a neurochemical mediator by the nerve endings in the skin, leading to inhibition of melanogenesis and destruction of melanocytes. • Self-destruction theory - proposes that melanocytes are destroyed by toxic melanin precursors such as free radicals. Experimental evidence is based on the fact that a number of chemicals induce pigmentary changes indistinguishable from vitiligo. • Autoimmune hypothesis - based on the observation that patients with vitiligo have an associated autoimmune disease in up to between 15– 30% of cases. 10
  • 11.
    1.1. Vitiligo… • Histologicalfeatures • complete absence of melanocytes in association with total loss of epidermal pigmentation. • Biopsies from the periphery of lesions with a clinically inflammatory border show lymphocytes and histiocytes in the papillary dermis. • Some inflammatory cells may also be found at the periphery, even in the absence of a clinically inflamed border. • At the advancing border, the melanocytes may be increased in size with an increased number of dendrites. 11 S-100 protein
  • 12.
    1.1. Vitiligo… • Differentialdiagnosis • Guttate hypomelanosis- clinical presentation and the complete absence of melanocytes in vitiligo, and the persistence of at least some melanocytes in the former. • Post inflammatory hypopigmentation- preservation of melanocytes with only loss of pigment. 12
  • 13.
    1.2. Oculocutaneous Albinism •A genetically heterogeneous group of disorders in which there is a generalized decrease or absence of melanin pigment in the eyes, hair, and skin. • At least 10 forms of this condition have been identified, each presumably resulting from a different biochemical block in the synthesis of melanin. • The most common forms are types 1 and 2, which account for 40% and 50%, respectively, of cases worldwide. • Type 1A is due to complete absence of tyrosinase activity in melanocytes whereas in type 1B there is reduced activity of tyrosinase. • Oculocutaneous albinism type 2 is caused by mutations in the gene OCa2. The OCa2 protein is important in the formation of melanosomes and in transport of melanosomal proteins. 13
  • 14.
    1.2. Oculocutaneous Albinism… •The clinical manifestations of oculocutaneous albinism depend on the type of biochemical abnormality. • In all types of albinism, the lack of melanin in the developing eye results in hypoplasia of the fovea and abnormal routing of the optic nerves. • As a result, all patients have variable strabismus, nystagmus, and reduced visual acuity. • Affected patients often have an increased risk of skin cancer. • Based on clinical features alone, it is not always possible to separate the different types of oculocutaneous albinism. • The clinical presentation at birth is white hair and skin and blue eyes. 14
  • 15.
    1.2. Oculocutaneous Albinism… •Histological features • Reduced or complete absence of melanin in the epidermis and hair follicles, depending on the type of oculocutaneous albinism. • Melanocytes are normal in number and morphology. • Tyrosinase activity is lacking in melanocytes in freshly plucked anagen hair bulbs in type 1A; it is reduced in heterozygotes with this phenotype and variably reduced in some of the other types. • Tyrosinase activity is normal in type 2. 15
  • 16.
    1.3. Tuberous Sclerosis:Hypopigmented Macules (“Ash Leaf Spots”) • Tuberous sclerosis is characterized by the triad of epilepsy, mental retardation, and multiple angiofibromas. • In addition, circumscribed macules of hypopigmentation known as “ash leaf spots” can be present at birth on the trunk and lower extremities. • The basic abnormality appears to be an arrest in the maturation of melanosomes. • They vary in diameter from 1 mm to 12 cm. • The more common shapes are oval, polygonal, or ash leaf–like. 16
  • 17.
    1.3. Tuberous Sclerosis:Hypopigmented Macules (“Ash Leaf Spots”)… • Histopathology • Numbers of melanocytes are not decreased in the hypopigmented macules, which can be confirmed with melan-A staining. • Epidermal melanin is reduced but not absent. 17
  • 18.
    1.4. Piebaldism • Arare congenital disorder inherited in an autosomal dominant manner. • There are nonprogressive, discrete patches of leukoderma. • The central area of the forehead, the anterior trunk, and the mid areas of the extremities are characteristically affected. • The hands, feet, and back are usually spared. • In 90% of cases there is a white forelock in the frontal mid scalp; this may be the only manifestation of the disease. • Café-au-lait spots are a frequent finding. An association with neurofibromatosis type 1 has been documented. 18
  • 19.
    1.4. Piebaldism… • Histologicalfeatures • complete absence of melanocytes • Abnormal melanocytes may be seen in areas of transition between involved and normal skin. • These melanocytes may have spherical melanosomes. • Some clear cells, representing Langerhans cells, are usually present in the epidermis. 19
  • 20.
    1.5. Pityriasis Alba •One of the most common localized disorders of hypopigmentation in children. • Young adults may also be affected. • Slightly more common in dark-skinned atopic males. • Ill-defined, slightly scaly patches of hypopigmentation on the face with predilection for the cheeks. • Also seen on the neck and shoulders. 20
  • 21.
    1.5. Pityriasis Alba… •Histologically, the changes are often subtle and consist of mild hyperkeratosis, focal parakeratosis, minimal spongiosis, and variable exocytosis of lymphocytes. • This is associated with mild loss of melanin in basal keratinocytes but not in the number of melanocytes. • In the dermis there is mild pigment incontinence and a sparse superficial, perivascular lymphohistiocytic inflammatory cell infiltrate. 21
  • 22.
    1.6. Idiopathic GuttateHypomelanosis • a common leukodermic dermatosis of unknown cause. • Multiple hypochromic macules, 2 to 5 mm in diameter which develop over many years. • Usually found on the sun- exposed extremities of elderly individuals. • Repigmentation does not occur. 22
  • 23.
    1.6. Idiopathic GuttateHypomelanosis… • Variable loss of melanin granules in epidermal keratinocytes. This is sometimes associated with epidermal atrophy and flattening of the rete ridges. • Orthokeratotic hyperkeratosis in a basket-weave pattern has also been documented. • However, complete loss of melanocytes is not a feature. 23
  • 24.
    1.6. Idiopathic GuttateHypomelanosis… • DDx- lichen sclerosus, hypopigmented mycosis fungoides, atrophie blanche, vitiligo, pityriasis versicolor, leprosy, and the hypopigmented lesions seen in tuberous sclerosis. • Most of these entities are easy to exclude histologically except for vitiligo. • In the latter there is complete absence of melanocytes and this can be confirmed with a melanocyte-specific immunostain such as Melan- a, since S-100 also stains Langerhans cells. 24
  • 25.
    1.7. Postinflammatory Hypopigmentation •Inflammation of the skin can result in hyperpigmentation or hypopigmentation. • Postinflammatory hypopigmentation is a very common form of hypopigmentation. • The lack of pigment becomes noticeable as the primary lesion fades. • The lesion is usually a macule with indistinct borders and a variable degree of hypopigmentation. 25
  • 26.
    1.7. Postinflammatory Hypopigmentation… •Histologically, there is focal reduction in pigmentation in the basal cell layer of the epidermis. • Residual features of the preceding or concurrent inflammatory dermatosis may also be present. • The diagnosis is usually obvious by the patient’s report of a previous inflammatory lesion at the sites of hypopigmentation. • When no such history can be obtained, the differential diagnosis includes halo nevus, pityriasis alba, pityriasis versicolor, and cutaneous infections such as those resulting from Candida spp. or dermatophytes. • Careful histopathologic examination for the presence of nevus cells and microorganisms should aid in distinguishing postinflammatory hypopigmentation from halo nevus and infectious processes, respectively. 26
  • 27.
    2. Disorders CharacterizedBy Hyperpigmentation • The following subclassification provides a useful approach to a biopsy from hyperpigmented lesions: 1. Disorders with basal hyperpigmentation: melasma, acquired brachial dyschromatosis, ephelis (freckle), café-au-lait spots, macules of Albright’s syndrome, Laugier–Hunziker syndrome, Peutz–Jeghers syndrome, and Becker’s nevus (melanosis)… 2. Disorders with epidermal changes: Dowling–Degos disease, Kitamura’s disease, and confluent and reticulated papillomatosis of Gougerot–Carteaud… 3. Disorders with striking melanin incontinence: postinflammatory melanosis, prurigo pigmentosa, generalized melanosis in malignant melanoma… 4. Disorders with melanin incontinence and epidermal atrophy or “dyskeratotic” cells: dyskeratosis congenita, frictional melanosis, active fixed drug eruptions, and active prurigo pigmentosa… 27
  • 28.
    2.1. Melasma (chloasma) •An acquired, chronic, recurrent lesion that develops in some women, especially those living in areas of intense UV radiation, who are pregnant or taking oral contraceptives. • Its incidence in pregnancy varies from 15% to 50%. • An association has also been documented with cosmetics, phototoxic drugs, isotretinoin, and anticonvulsants. • Melasma also occurs, though less commonly, in men. • There is a marked predilection for the face (forehead and cheeks). • Symmetrical hyperpigmentation characterized by irregular light to dark-brown confluent or speckled macules with sharply demarcated margins involving sun-exposed skin. 28
  • 29.
    2.1. Melasma… • Histologically,there is increased melanin in the epidermis, particularly in the basal layers. • Melanin pigment is located in a “cap” overlying the keratinocyte nuclei. • Normal melanocyte numbers in all cases. • However, melanocytes are enlarged and have increased numbers of dendrites. • Mild pigment incontinence is sometimes present, along with a perivascular lymphohistiocytic infiltrate and increased vascularity. • Solar elastosis is more prominent than in normal skin. • Mast cells are also increased in number. 29
  • 30.
    2.2. Cafe´-au-lait spots •“coffee-with-milk” • They may be present at birth or develop within the first few years of life. • They are found in approximately 15% of individuals. • They are not increased in patients with tuberous sclerosis. • Multiple café-au-lait spots are a feature of neurofibromatosis (95% of NF1 patients). Axillary freckling is often also present in these cases. • Café-au-lait spots have also been reported in Bloom’s syndrome, Cowden’s disease, Fanconi’s anemia, ring chromosome syndromes, ataxia–telangiectasia, nevoid BCC syndrome, Legius syndrome, and Noonan’s syndrome. • Uniformly pigmented, tan to dark brown macules with well- defined borders that vary in size from small, freckle-like lesions to large patches 20 cm or more in diameter. 30
  • 31.
    2.2. Cafe´-au-lait spots… •An increase in melanin pigment deposition within basilar keratinocytes. • The density of melanocytes is normal or only slightly increased. • The increased pigmentation typically spares the adnexal epithelium. • Giant melanin granules (macromelanosomes) can be seen in café-au-lait spots in many patients with neurofibromatosis. • The diagnostic significance of macromelanosomes is diminished by their absence in some children with neurofibromatosis and their presence in normal skin and other pigmented macular lesions. 31
  • 32.
    2.2. Cafe´-au-lait spots… •Differential diagnosis • Postinflammatory hyperpigmentation, melasma, melanocytic nevi. • Café au-lait macules have a tendency to grow in proportion to growth of the rest of the body. • They do not change with sun protection or bleaching agents. • Their completely macular appearance may be helpful for the correct diagnosis. • Histologically café-au-lait macules are usually indistinguishable from freckles, melasma, and the melanotic macules of Albright’s syndrome. • They can be differentiated from melanocytic nevi and simple lentigines by their lack of melanocyte proliferation and rete ridge elongation. • Café-au-lait macules differ from lesions of postinflammatory hyperpigmentation by the presence of an inflammatory infiltrate or pigment incontinence in the latter. 32
  • 33.
    2.3. Ephelis (Freckle) •Ephelides (freckles) are small, well-defined, pigmented macules 1 to 2 mm in diameter. • Show predilection for the face, arms, and shoulder regions of fair- skinned individuals. • They appear at an early age and may follow an episode of severe sunburn. • Darken easily with sun exposure. 33
  • 34.
    2.3. Ephelis (Freckle)… •The epidermis appears normal in structure. • The basal cells in the affected areas are more heavily pigmented with melanin than those in the surrounding skin. • There is usually sharp delimitation of the abnormal areas from the normal. • There are normal numbers of melanocytes. • No elongation of rete ridges and no nests. 34
  • 35.
    2.4. Macules OfAlbright’s Syndrome • Albright’s syndrome is characterized by the triad of polyostotic fibrous dysplasia, sexual precocity—especially in the female, and pigmented macules. • These macules are large, often unilateral, and related to the side of the bone lesions. • The outline of the macules is very irregular, in contrast to that of café-au-lait spots. • They mainly involve the trunk and proximal lower limbs and less commonly the face and neck. 35
  • 36.
    2.4. Macules OfAlbright’s Syndrome… • A skin biopsy from a pigmented macular lesion resemble freckles, showing hyperpigmentation of the basal layer. • Giant melanosomes are sometimes seen but are not as frequent as in the café-au-lait spots of neurofibromatosis type I. • In the dermis and subcutaneous tissue, plaque-like osteomas may be seen. 36
  • 37.
    2.5. Becker’s Nevus(melanosis) • Is usually found in the region of the shoulder girdle as unilateral, hyperpigmented areas of somewhat thickened skin. • The male-to-female ratio ranges from 4-6 : 1. • It is more common in young people with fair skin. • Occasionally, lesions have been said to follow severe sunburn. • Hypertrichosis may develop after the pigmentation, but is not invariable. • May be associated with connective tissue nevus, accessory scrotum, areolar hypoplasia. 37
  • 38.
    2.5. Becker’s Nevus... •The epidermal changes are variable, but usually there is acanthosis and sometimes mild papillomatous hyperplasia. • Elongated rete ridges with pointed or flat tips. • There is variable hyperpigmentation of the basal layer with some melanophages in the dermis. • Melanocyte proliferation is usually mild and not always obvious in routine sections; special studies have shown a quantitative increase. 38
  • 39.
    2.6. Postinflammatory Melanosis •Hyperpigmentation may follow a number of inflammatory dermatoses, particularly those involving damage to the basal layer. • Thus, it may follow various disorders that present a lichenoid reaction pattern, such as lichen planus, lichenoid drug eruptions, and fixed drug eruptions. • Specific drugs that may cause postinflammatory and/or increased basal pigmentation include the following: prostaglandin analogs, interferon-α, olanzapine, hydroxyurea, and calcipotriol. 39
  • 40.
    2.6. Postinflammatory Melanosis… •There are two major histopathological types of postinflammatory hyperpigmentation: Epidermal- increased basilar epidermal pigmentation, and Dermal- marked pigmentation in the upper dermis and decreased epidermal pigmentation. • More prominent perivascular lymphocytic inflammation is seen in the dermal pigment group. • Basal pigmentation is prominent in photodermatitis. 40
  • 41.
    2.7. Laugier-Hunziker Syndrome •An acquired disorder characterized by macular pigmentation of the lips, oral cavity (mainly hard palate and less commonly buccal mucosa, soft palate, and gums) and, less frequently, fingers and palms. • Longitudinal melanonychia is seen in up to 50% of patients. • Genital and conjunctival pigmentation is very rare. • The sex incidence is similar and most patients are Caucasian and middle aged. 41
  • 42.
    2.7. Laugier-Hunziker Syndrome… •Histologically, there is hyperpigmentation of basal keratinocytes and pigment incontinence with melanophages in the papillary dermis. • Recently, it has been suggested that there is an increase in the number of basal dendritic melanocytes and the term ‘mucocutaneous lentiginosis of Laugier and hunziker’ has been proposed. 42
  • 43.
    References • Weedon’s SkinPathology, Fifth Edition • McKee's Pathology of the Skin, Fourth Edition • FDP Dermatopathology, Second Edition • Fitzpatrick’s Dermatology, Ninth Edition 43

Editor's Notes

  • #12 1.Melanocytes and melanin are absent from the basal layer. 2. Vitiligo: There is complete absence of melanocytes and melanin pigment. 3. Vitiligo. There is complete absence of both melanocytes and melanin. 4. Vitiligo. A melanocyte with a giant melanosome is present at the edge of the depigmented area 5. Vitiligo: skin biopsy from lesional skin stained with S-100 protein.