Porphyrias are inherited or adquired diseases that result from an abnormal metabolism of heme biosynthesis pathway. The main causes are enzyme deficiencies that lead to heme pathways intermediates accumulation. Heme biosynthesis occurs almost entirely in the liver and bone marrow and is composed by eight reactions, each one of these being catalyzed by an especific enzyme. Therefore, partial or complete deficiency of one of these enzymes result in diferents clinical pictures. We will focus our discussion mainly on clinical grounds.
There are two major groups of porhyrias according to the site where dysfunction occurs, i.e, hepatic and erythropoietic porphyrias. Among erythropoietic types, there are: Congenital Erythropoietic Porphyria and Protoporphyria. Hepatic porphyrias are: Intermitent Acute Porphyria, Hereditary Coproporphyria, Variegate Porphyria and Porphyria Cutanea Tarda. It is important to recognize that the three most common types of porphyrias are Intermitent Acute Porphyria (IAP), Porphyria Cutanea Tarda (PCT) and Protoporphyria (PP).
Clinical Manifestations and Diagnosis
Intermitent Acute Porphyria: The majority of patients are assymptomatic. Signs and symptoms rarely start before puberty. The initial and commonest manifestation is abdominal pain, which can be diffuse or localized, colicky. The clinical picture may mimic an accute inflammatory abdominal disease. It is caused by an altered autonomic activity. Peripheral neuropathy is primarily motor, beginning in proximal muscles, more often in the arms. Cranial nerves manifestations my lead to optic nerve atrophy. CNS abnormalities include seizures, delirium and coma. Hepatic dysfunctions are common. Precipitating factors are drugs as barbiturates, sulfonamides, estrogens and dietary restriction of carbohydrates. Diagnosis is made on clinical grounds and increased erythrocytic and urinary porphobilinogen and aminolevolinic acid (ALA) levels (metabolic intermediates of heme).
Treatment is based on large amounts of glucose administration and intravenous infusion of hematin once daily for 4 days. It is important to avoid precipitating factors such as drugs mentioned before and fasting.
Hereditary Coproporphyria (HC) : Clinical manifestations are identical to IAP, except for cutaneous photosensitivity that occurs in one third of cases. During acute attacks, it is impossible to distinguish clinically and laboratorially HC from IAP. Treatment is the same of IAP.
Porphyria Cutanea Tarda (PCT) : PCT is the most common form of porphyria. It is an adquired disorder, associated with estrogen and alcohol use. Photosensitivity is the only major manifestation. Cutaneous manifestations are dermoabrasions, superficial erosions and blister formation after trivial mechanical trauma. The lesions leave depigmented and pigmented scars. Hypertricosis and hirsutism may occur.
Diagnosis can not be stabilished on clinical grounds. Therefore it is essential to measure metabolites of heme as uroporphirin and 7-carboxilase porphyrin in urine and coproporphyrin in feces. Repeated phlebotomies is the treatment of choice. Chloroquine is useful when phlebotomies are contraindicated. Alcohol and estrogen should be discontinued.
Variegate Porphyria (VP) : Neurologic manifestations are the same of IAP and cutaneous manifestations are similar to PCT. Diagnosis is made on laboratory findings such as urinary coproporphyrin. Treatment is obtained with glucose administration and hematin infusion.
Protoporphyria (PP) : Mild photosensitivity occurs after sunlight exposition and is characterized by painful burning or stinging sensations, pruritus, erythema, and occasional edema. This is a distinct picture from other porphyrias. Mild abnormalities in liver, biliary tract and blood may be present. Diagnosis is made by detection of protoporphyrin in erytrhocytes. ALA and PBG are usually normal in urine. Carotene oral administration is the main staim of treatment.
Congenital Erytrhopoietic Porphyria (CEP) : Photosensitivity, splenomegaly and hemolitic anemia are the solely manifestations. Hypertrichosis and erythrodontia are also common. The urine contains high amounts of uroporphyrin I, coproporphyrin. Treatment is based on oral carotenoids and sunlight exposition avoiding. It is important to remember that CEP is extremmely rare, with less than 200 cases reported.