Sarcoidosis

Cutaneous manifestations

•    Lupus pernio:

o    Violaceous, indurated plaques on nose, cheeks, lips, ears

o    Strongly associated with upper respiratory tract involvement

•    Papules, plaques, nodules

o    Often on face and extremities

•    Erythema nodosum

o    Tender, erythematous nodules on shins

o    Suggests acute, self-limiting disease, usually good prognosis

Pearls

•    Non-caseating granulomas on biopsy

•    ACE level often raised; consider pulmonary involvement

Porphyrias

Porphyria cutanea tarda (PCT)

•    Blistering photosensitive skin lesions

•    Hyperpigmentation, hypertrichosis (especially face)

•    Skin fragility, milia formation

•    Exacerbated by alcohol, oestrogens, hepatitis C, iron overload

Diagnostics

•    Urine: pink or orange fluorescence under Wood's lamp (uroporphyrins)

Treatment

•    Phlebotomy (reduce iron stores)

•    Low-dose hydroxychloroquine

Diabetes Mellitus

Cutaneous manifestations

•    Necrobiosis lipoidica

o    Yellow-brown, atrophic plaques with telangiectasia

o    Commonly on shins

o    Ulceration possible

•    Candidiasis

o    Intertriginous areas (axillae, groin, under breasts)

o    Vulvovaginal candidiasis frequent in women

•    Acanthosis nigricans

o    Hyperpigmented, velvety thickening

o    Neck, axillae

o    Insulin resistance marker; in rare cases, may indicate gastric adenocarcinoma

•    Diabetic dermopathy

o    "Shin spots": brown, atrophic macules

Amyloidosis

Cutaneous signs

•    Waxy papules and plaques

o    Periorbital, anogenital

•    Pinch purpura

o    Easy bruising from minimal trauma (especially around eyes)

•    Macroglossia (seen in systemic amyloidosis)

Pearls

•    AL amyloidosis often associated with plasma cell dyscrasias (e.g., myeloma)

Thyroid Disease

Hyperthyroidism

•    Pretibial myxoedema (Graves' dermopathy)

o    Localised, firm, non-pitting oedema

o    Shins most common

•    Alopecia areata: patchy hair loss

Hypothyroidism

•    Dry, coarse skin

•    Hair thinning, loss of lateral eyebrows

•    Myxoedema (generalised skin thickening)

Chronic Kidney Disease (CKD)

Cutaneous manifestations

•    Pruritus

o    Very common in advanced CKD

o    May be due to secondary hyperparathyroidism, uraemic toxins

•    Calciphylaxis (calcific uraemic arteriolopathy)

o    Painful, purpuric skin lesions → ulceration, necrosis

o    High mortality; often in dialysis patients

o    Risk factors: hyperphosphataemia, hypercalcaemia, warfarin use

•    Skin pigmentation changes

o    Yellowish or brownish due to carotene accumulation and hyperpigmentation

Extra Revision Pearls

•    Lupus pernio → specific for sarcoidosis

•    Acanthosis nigricans → think insulin resistance first; if sudden and widespread, rule out internal malignancy

•    PCT + hepatitis C + alcohol → classic exam trio

•    Calciphylaxis → do not biopsy ulcer edge → risk of worsening necrosis