Contents
 

Disorders of melanin pigmentation



5  Non-tumorous skin diseases

5.22  Disorders of melanin pigmentation

Introduction:

Processes, characterized by increased or decreased melanin pigmentation.

5.22.1  Vitiligo

Clinical signs:

  • areas under mechanic stress: perioral and periorbital skin, neck, wrists, ankles, dorsa of the hands, breasts etc.
  • sharply demarcated macules, merging into larger lesions
  • smooth surface, no scales
  • usually depigmentation of the hairs as well
  • possible repigmentation from the follicles

Histology:

The number of melanocytes within the epidermis is decreased or there are no melanocytes at all. Variable lymphocytic infiltration, usually mild and often none.

5.22.2  Hypomelanosis guttata

Clinical signs:

  • sharply circumcscripted white macules, size about 5 mm
  • location: sun exposed skin

Histology:

Inconspicuous; Fontana-Masson staining reveals pigment reduction; the number of melanocytes is decreased.

5.22.3  Pityriasis alba

salba

Clinical signs:

  • hypopigmented patches
  • location: upper trunk
  • may follow eczema, but etiology is unknown

Histology:

The signs are inconstant: mild hyperkeratosis, parakeratosis, spongiosis. Melanocytes are normal, the amount of melanin is reduced.

Pictures

Pityriasis alba:
Pityriasis alba, HE 40x (6238)

Pityriasis alba:
Pityriasis alba, HE 40x (6239)

5.22.4  Albinism

Clinical signs:

  • oculocutaenous albinism
    • tyrosinase positive: the most frequent variant; complete at first, later small amount of melanin is formed
    • tyrosinase negative: complete albinism
  • photophobia, vision disorders
  • squamous cell carcinomas appear on sun exposed areas of the body
  • frequency: 1:10 000

5.22.5  Melasma, chloasma

Clinical signs:

  • acquired pigmented macules
  • location: face, symmetric
  • often associated with pregnancy, aggravated by sunlight

Histology:

Hyperpigmented basal layer of the epidermis with slightly increased number of melanocytes. Some pigment is present within the papillary dermis as well (free pigment, scattered melanophages).

Pictures

Melasma:
Melasma, HE 40x (2301)

5.22.6  Ephelides, freckles

Clinical signs:

  • small brown macules
  • location: face, shoulders
  • darken with sunburn

Pictures

Ephelides (frecles):
Ephelis, CLINIC (2891)

Histology:

Hyperpigmentation of the epidermal basal layer; number of melanocytes is normal.

5.22.7  Melanocytic macule of the lip or genital

Clinical signs:

  • pigmented macule in variable shades of brown
  • size up to 15 mm
  • localization: lip, genital (vulva, penis)

Histology:

Acanthosis, dendritic melanocytes, increased pigmentation of the basal layer of the epidermis. Melanophages are scattered in the papillary dermis in about half of cases.

Pictures

Melanocytic macule of the lip (labial lentigo):
Melanotic macule of the lip, HE 40x (4052)

Melanocytic macule of the lip, another case:
Melanotic macule of the lip, HE 40x (2300)

Genital lentigo:
Genital lentigo, HE 20x (4263)

5.22.8  Dowling-Degos disease

Clinical signs:

  • reticular hyperpigmentation of flexural areas (cubital and popliteal fossae, axillae, lateral aspects of the neck, inguinae etc.)
  • congenital, dominantly inherited disease

Histology:

Hyperpigmentation of the basal layer, the number of melanocytes is normal or slightly increased.

Pictures

Dowling-Degos disease, pigmentary incontinence:
Dowling-Degos disease, HE 10x (1258)

Dowling-Degos disease, HE 20x (1259)

Another case:
Dowling-Degos disease, HE 20x (4469)

5.22.9  Melanodermatitis toxica, melanosis Riehl

Clinical signs:

  • pigmented patches, usually permanent
  • location: face (forhead, cheeks)

Etiology:

  • variable toxic substances

Histology:

Vacuolar degeneration, epidermal atrophy, melanophages scattered in the upper dermis.

Pictures

Melanodermatitis toxica:
Melanodermatitis toxica, HE 20x (4806)

5.22.10  Incontinentia pigmenti

Clinical signs:

  • rare genodermatosis
  • affects the skin and other organs (CNS, eye, skelet and others)
  • 3 stages:
    1. spongiosis with eosinophils, necrotic keratinocytes
    2. verrucous stage: mild acanthosis and papillomatosis, dyskeratoses
    3. incontinence of melanin

For details see special literature.

Pictures

Pigment incontinence, third stage:
Incontinentia pigmenti, third stage, HE 40x (4737)
  [zoomify]

5.22.11  Nevus achromicus

Clinical signs:

  • hypopigmented macule
  • age: inborn, children
  • location: trunk, proximal parts of the extremities

Histology:

Normal or slightly reduced melanocytes.



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