12.6 Pigment Disorders, Alopecia, Nail Disease & Photosensitivity
Key Takeaways
- Pigment disorders, alopecia, disorders of the nails and photosensitivity dermatoses are four separate named blueprint subsections.
- Vitiligo is associated with autoimmune thyroid disease, type 1 diabetes, pernicious anemia and Addison disease.
- Sudden extensive acanthosis nigricans in an older adult suggests underlying malignancy, most often gastric adenocarcinoma.
- Telogen effluvium follows a physiologic stressor by two to three months and produces diffuse non-scarring shedding that recovers spontaneously.
- Porphyria cutanea tarda causes painless blistering of sun-exposed skin and is associated with hepatitis C, HIV, alcohol, estrogen and iron overload.
1. Pigment Disorders
Vitiligo
Autoimmune destruction of melanocytes producing sharply demarcated, completely depigmented macules and patches, often symmetric and favoring the face, hands, and periorificial and acral sites. Depigmentation is chalk-white and accentuated on Wood lamp examination, distinguishing it from the merely hypopigmented lesions of tinea versicolor or post-inflammatory change.
The exam value is the association list. Vitiligo is a marker of autoimmune diathesis:
- Autoimmune thyroid disease — the most frequent association; check thyroid-stimulating hormone
- Type 1 diabetes mellitus
- Pernicious anemia
- Addison disease
- Alopecia areata
Treatment includes topical corticosteroids and calcineurin inhibitors, phototherapy, and newer JAK inhibitor topicals; sun protection is essential because depigmented skin burns readily.
Melasma
Symmetric brown patches on the malar cheeks, forehead and upper lip, driven by estrogen and ultraviolet exposure — hence pregnancy (chloasma, the mask of pregnancy) and combined oral contraceptives. Treatment is rigorous photoprotection, hydroquinone, retinoids and removal of the hormonal trigger. It recurs readily with sun exposure.
Acanthosis nigricans
Velvety, hyperpigmented thickening of intertriginous skin — neck, axillae, groin — often with skin tags.
| Pattern | Implication |
|---|---|
| Gradual, obesity-associated | Insulin resistance — the common form; screen for diabetes |
| Drug-induced | Nicotinic acid, systemic corticosteroids, insulin, oral contraceptives |
| Sudden, extensive, with mucosal or palmar involvement | Malignancy, most often gastric adenocarcinoma |
Rapid-onset, widespread acanthosis nigricans in a non-obese adult, especially with weight loss or involvement of the palms (tripe palms) or oral mucosa, warrants a malignancy evaluation.
Xeroderma pigmentosum
An enumerated topic: an inherited defect in nucleotide excision repair causing extreme ultraviolet sensitivity, severe photodamage from childhood and markedly elevated rates of skin cancer at a young age. Management is absolute photoprotection and lifelong dermatologic surveillance.
2. Alopecia
The first determination is scarring versus non-scarring, because scarring alopecia destroys follicles permanently and demands urgent treatment.
| Non-scarring | Scarring (cicatricial) | |
|---|---|---|
| Follicular openings | Preserved | Lost — smooth shiny scalp |
| Reversibility | Potentially reversible | Permanent |
| Examples | Androgenetic, telogen effluvium, alopecia areata, tinea capitis, traction, trichotillomania | Discoid lupus, lichen planopilaris, central centrifugal cicatricial alopecia, folliculitis decalvans |
Loss of follicular ostia means scarring alopecia and warrants prompt dermatologic referral and biopsy.
Common non-scarring patterns
- Androgenetic alopecia — patterned recession and vertex thinning in men, diffuse widening of the central part with preserved frontal hairline in women. Treated with topical minoxidil and, in men, finasteride.
- Telogen effluvium — diffuse shedding beginning two to three months after a stressor: major illness, surgery, childbirth, severe weight loss, iron deficiency, thyroid disease, or a new drug. A positive hair pull test yields telogen (club) hairs. It recovers spontaneously once the trigger is corrected; the treatment is reassurance plus correcting iron deficiency or thyroid dysfunction.
- Alopecia areata — sharply circumscribed round patches of complete hair loss with exclamation-point hairs at the margin. Autoimmune, associated with thyroid disease and vitiligo. May progress to alopecia totalis or universalis. Treated with intralesional corticosteroids and, in extensive disease, JAK inhibitors.
- Tinea capitis — scaling with broken hairs and often occipital lymphadenopathy. Requires oral antifungal therapy; topical agents do not penetrate the follicle.
- Traction alopecia — from tight hairstyles; reversible early, scarring if prolonged.
In any woman with diffuse hair loss, check ferritin, thyroid-stimulating hormone and complete blood count, and consider androgen excess if there is hirsutism or menstrual irregularity.
3. Disorders of the Nails
A named blueprint subsection. Nails are a window into systemic disease, and the exam uses them as diagnostic clues.
| Finding | Description | Associations |
|---|---|---|
| Clubbing | Loss of the normal nail-fold angle, sponginess | Lung cancer, bronchiectasis, cystic fibrosis, interstitial lung disease, cyanotic heart disease, inflammatory bowel disease, cirrhosis; not COPD alone |
| Koilonychia | Spoon-shaped concavity | Iron deficiency |
| Beau lines | Transverse grooves | A systemic insult that arrested growth; timing estimable from position |
| Onycholysis | Distal separation from the bed | Psoriasis, thyrotoxicosis, trauma, photo-onycholysis from tetracyclines |
| Nail pitting | Fine punctate depressions | Psoriasis, alopecia areata |
| Terry nails | Proximal white with a distal pink band | Cirrhosis, heart failure, diabetes |
| Half-and-half (Lindsay) nails | Proximal white, distal brown | Chronic kidney disease |
| Muehrcke lines | Paired transverse white bands that do not move with growth | Hypoalbuminemia |
| Splinter hemorrhages | Linear subungual streaks | Trauma most often; endocarditis, vasculitis |
| Longitudinal melanonychia | Pigmented band | Benign in darker skin; worrying if single, widening, irregular, or with Hutchinson sign |
Hutchinson sign — extension of pigment onto the proximal nail fold — suggests subungual melanoma and requires biopsy. A single new widening pigmented band in a lighter-skinned adult should not be dismissed.
Onychomycosis should be confirmed before treating, by potassium hydroxide preparation, culture or PAS staining, because psoriasis, lichen planus and trauma mimic it and systemic antifungals carry hepatotoxicity and drug interaction risk. Terbinafine is the usual oral agent.
Chronic paronychia is an inflammatory condition of wet-work exposure rather than a bacterial infection, and is treated with irritant avoidance and topical steroids; acute paronychia is bacterial and may require drainage.
4. Photosensitivity Dermatoses
A named blueprint subsection listing porphyria cutanea tarda and photodermatitis.
Drug-induced photosensitivity
| Phototoxic | Photoallergic | |
|---|---|---|
| Mechanism | Direct tissue injury | Type IV hypersensitivity |
| Onset | Minutes to hours; first exposure | Requires prior sensitization; 24 to 72 hours |
| Appearance | Exaggerated sunburn, sharply limited to exposed skin | Eczematous, may spread beyond exposed skin |
| Frequency | Common | Uncommon |
| Classic drugs | Doxycycline, fluoroquinolones, amiodarone, thiazides, NSAIDs, voriconazole | Sunscreen agents, fragrances, topical NSAIDs |
Doxycycline photosensitivity is the archetype and should be mentioned whenever it is prescribed for acne or tick-borne illness in summer. Photo-onycholysis is a distinctive tetracycline effect.
Porphyria cutanea tarda
The most common porphyria and a purely cutaneous one.
- Painless blistering and skin fragility on sun-exposed skin, especially the dorsal hands, with erosions, milia, scarring and hypertrichosis of the face
- No abdominal pain, no neuropathy — the contrast with acute intermittent porphyria
- Urine may fluoresce coral-pink under Wood lamp
A new diagnosis obliges an etiologic search: hepatitis C, HIV, alcohol, estrogen therapy, smoking, and iron overload including HFE mutations. Diagnosis is by elevated urinary uroporphyrins. Treatment is repeated phlebotomy or low-dose hydroxychloroquine with sun protection and removal of the precipitant; curing hepatitis C often resolves it.
Other photodermatoses
- Polymorphous light eruption — the most common idiopathic photodermatosis. Pruritic papules and plaques appearing hours to days after the first substantial sun exposure of the season, with subsequent hardening as the summer progresses.
- Solar urticaria — wheals within minutes of exposure.
- Photoaggravated disease — subacute cutaneous lupus erythematosus presents with annular or papulosquamous lesions in a photodistribution, is strongly associated with anti-Ro (SSA), and is a well-recognized drug-induced entity (hydrochlorothiazide, terbinafine, proton pump inhibitors, tumor necrosis factor inhibitors). Dermatomyositis produces a photodistributed violaceous eruption with the heliotrope rash and Gottron papules.
A 62-year-old man with a body mass index of 24 kg/m2 develops velvety hyperpigmented thickening of the axillae, neck and groin over three months, with new thickening of the palms and involvement of the oral mucosa. He has lost 7 kg unintentionally. Fasting glucose and hemoglobin A1c are normal. What is the most appropriate next step?
A 44-year-old man presents with painless blistering and skin fragility on the dorsa of both hands, with several erosions, small milia and increased facial hair. He reports no abdominal pain and no neuropathy. He drinks four beers most nights. Which associated condition should be tested for?