A 47 Year Old man With A Blistering Rash On His Hands, Scalp And Face

A 47-year-old businessman was referred to the dermatology clinic with a rash over his hands, scalp and face. He had been generally well. He smoked 20 cigarettes per day and drank 8–10 units of alcohol on a daily basis. There was no other significant medical history of note. The patient had not taken any medication, with the exception of occasional chlorpheniramine to help relieve his
symptoms. On examination he had vesicular lesions affecting his face, forearms, hands and scalp. All other physical examination was essentially normal.

Blisters and fragility on the back of the hands.

What is the most probable diagnosis?
Porphyria cutanea tarda

Case Discussion:
Porphyria cutanea tarda (PCT) is a rare disorder of haem synthesis that is inherited as an autosomal dominant trait. Another acquired type is also described. 
Pathology: The primary cause of this disorder is a deficiency of uroporphyrinogen decarboxylase, a cytosolic enzyme that is the enzymatic pathway that leads to synthesis of heme. This enzyme catalyses the conversion of uroporphyrin to coproporphyrin. This leads to an excess of uroporphyrins in the blood and urine. The result is a
pruritic photosensitive blistering rash that affects areas exposed to sunlight, and cirrhosis of the liver. Blisters on
the skin lesion contain PAS-positive material. 

The clinical effect of this deficiency becomes most apparent in genetically predisposed patients who consume excess alcohol or other drugs that are enzyme-inducers for haem synthesis (most commonly anticonvulsants and oestrogens)

Clinical Features: The clinical symptoms may not begin immediately after exposure to sun, so some patients may not recognise that sun exposure is causing the symptoms. Patients experience chronic, recurring blisters of various sizes on face, scalp, arms and the back of the hands. The lesions heal slowly and with scarring. The skin especially on the hands is sensitive to minor injuries. Sometimes patients may observe swelling , itching or redness of theses sun exposed areas. Some patients may report discolored urine and changes in growth of body hair. 

Differential Diagnosis: include:

• Bullous Systemic Lupus Erythematosus.
• Congenital Erythropoietic porphyria
• Epidermolysis Bullosa
• Hydroa Vacciniforme
• Pseudoporphyria.

Diagnosis:

Urinary porphyrin levels are abnormally high in porphyria cutanea tarda patients, with several hundred to several thousand micrograms excreted in a 24-hour period. 

Treatment: Treatment is by abstaining from alcohol and avoiding sunlight. In patients with a high Hb, weekly venesection (not more than 1 unit) until the Hb is less than 12 g/dl helps to alleviate the skin manifestations. Chloroquine, which binds uroporphyrin and helps urinary clearance, is commonly used in the management.