Pigmentary, Hair, Nail, and Sweat Gland Disorders
Pigmentary disorders
Understand melanocyte biology: melanin synthesis, transfer via melanosomes, and the difference between melanocyte number and activity. Vitiligo is autoimmune melanocyte destruction with sharply demarcated depigmentation; Wood's lamp enhances. Melasma is hormonally and UV-driven, with increased melanocyte activity but normal numbers. Post-inflammatory hyperpigmentation follows injury. Albinism is genetic (tyrosinase and related genes) with systemic risk (photosensitivity, ocular changes).
Hair disorders
Classify as non-scarring (alopecia areata, androgenetic, telogen effluvium) versus scarring (lichen planopilaris, discoid lupus, folliculitis decalvans). Key signs: exclamation-mark hairs in alopecia areata, miniaturisation in androgenetic alopecia, and loss of ostia in scarring alopecia. Hirsutism versus hypertrichosis is a common discriminator.
Nail and sweat gland disorders
Nail findings map to disease: pitting (psoriasis), onycholysis, Beau's lines, subungual haematoma, and longitudinal melanonychia (melanoma warning). Sweat gland disorders include hyperhidrosis, miliaria, and hidradenitis suppurativa (follicular occlusion).
Traps
- Assuming all depigmentation is vitiligo - consider post-inflammatory and chemical leukoderma.
- Missing that scarring alopecia requires urgent biopsy and treatment.
- Confusing hirsutism (androgen-dependent terminal hair) with hypertrichosis (generalised excess hair).
Rule of thumb
For pigment loss, ask is it depigmented (melanocytes absent) or hypopigmented (melanocytes present but underactive)? That determines the differential.