Wednesday, November 5, 2014

A 19-year-old college freshman comes to the clinic complaining of blistering skin lesions on the back

A 19-year-old college freshman comes to the clinic complaining of blistering skin lesions on the back of his hands and arms that are painful. He’s noticed these occasionally during his childhood, and they were often precipitated by sunlight and healed with scarring. He now notices that since starting college they are more frequent, and often occur after drunken parties. His hands and forearms have numerous hypopigmented scars that he says are from previous episodes. The skin over the back of his hands appears thick and coarse. Otherwise his review of systems and physical examination is normal. The lesions on his hands are shown in Figure . Which of the following tests will most likely yield the correct diagnosis?

B. Anti-SCL-70
C. Plasma cortisol
D. Plasma porphyrin
E. Urine porphobilinogen


The answer is D. This patient has porphyria cutanea tarda (PCT). The major
clinical feature of PCT is scarring skin lesions predominantly affecting the back of the
hands that also may involve the forearms, face, legs, and feet. The lesions start as blisters
that rupture and crust over, leaving scarring. Chronically, the areas most involved can
develop thickened skin similar to systemic sclerosis. PCT is the most common porphyria;
it usually occurs sporadically, but there is also a familial form. It is due to a deficiency
of hepatic URO-decarboxylase, which must have more than 20% activity for symptoms.
Excess hepatic iron is involved in the pathogenesis, and phlebotomy aiming for a low
normal ferritin is a component of treatment. Precipitating factors should be avoided.
Episodes are typically provoked by alcohol intake or sun exposure.

 Plasma porphyrins should be measured in patients suspected of PCT. Urinary ALA may be slightly increased, but urinary porphobilinogen is normal. Urine porphobilinogen is elevated during attacks
of acute intermittent porphyria. ANA is utilized in the diagnosis of SLE, which may
present with photosensitivity. Anti-SCL-70 is used to diagnose systemic sclerosis, which
may also present with thick skin.


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