MKSAP Quiz: 6-week history of blisters


A 55-year-old man is evaluated for a 6-week history of blisters on his hands. The blisters are tender, break easily after they develop, and occur in different regions on the backs of his hands. Medical history is notable for alcoholic liver disease. The patient does not use tobacco but drinks 6 beers daily. He takes no medications.

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On physical examination, temperature is 36.4°C (97.5°F), blood pressure is 98/70 mm Hg, pulse rate is 85/min, and respiration rate is normal. BMI is 22. Cardiopulmonary examination is normal. The abdominal examination is significant for mild splenomegaly; there is no evidence of ascites. The patient has slight darkening of his skin and scattered spider telangiectasias. Mild hypertrichosis is evident on the face. The hand findings are shown.

There are no oral erosions or ocular inflammation.

Which of the following is the most likely diagnosis?

A: Allergic contact dermatitis

B: Bullous lupus erythematosus

C: Bullous pemphigoid

D: Porphyria cutanea tarda


Answer and critique

The correct answer is D. Porphyria cutanea tarda. This question can be found in MKSAP 17 in the Dermatology section, item 60.

This patient has porphyria cutanea tarda (PCT). PCT is a rare skin disease that typically occurs in the setting of underlying liver disease, which in this patient is likely due to heavy alcohol use. It may also develop in patients with chronic hepatitis C infection and hemochromatosis. PCT is caused by decreased activity of hepatic uroporphyrinogen decarboxylase, an enzyme in the heme biosynthesis pathway that leads to accumulation of porphyrins in the tissues. Only 20% of cases of PCT are due to inherited enzyme mutations, the remainder is acquired. The acquired forms appear to be related to increased oxidative stress in hepatocytes, possibly associated with iron deposition, although the exact mechanisms of decreased enzyme activity have not been elucidated. Patients with PCT often have darkening of the skin, hypertrichosis, and fragility of the skin, particularly in sun-exposed and frequently traumatized areas such as the dorsal hands. Numerous scars and small milia (tiny proteinaceous cysts) are often seen on the dorsal hands; intact blisters are rare, but often exist transiently before being spontaneously ruptured following mild trauma.

Allergic contact dermatitis may lead to blisters, but not scarring or milia, and there is no history to suggest an environmental trigger in this patient. The lesions of contact dermatitis typically will be sharply demarcated and geometric in appearance, corresponding to the area affected by the causative agent.

Bullous lupus erythematosus is a rare form of cutaneous lupus in which patients develop small blisters within and in addition to their other cutaneous lupus lesions; the blisters are generally small and often rupture with some residual dyspigmentation and scarring. Signs of systemic lupus erythematosus should be present when making a diagnosis of bullous lupus erythematosus.

Bullous pemphigoid is an autoimmune blistering disease common in the elderly that presents with urticarial plaques and tense, intact bullae; there is no association with liver disease.

Key Point

  • Porphyria cutanea tarda, which may develop from extensive alcohol use, hemochromatosis, or hepatitis C virus infection, presents with skin fragility and small, transient, easily ruptured vesicles in sun-exposed areas, such as on the hands.