QUESTION OF THE DAY
A 21-year-old young woman, who recently began taking birth control pills, presents to the emergency room with cramping abdominal pain, anxiety, paranoia, and hallucinations. A surgical evaluation, including ultrasound and computed tomography (CT) scan, fails to demonstrate an acute abdominal process. A urinalysis reveals an increase in urine porphyrins. Which of the following is the most likely defect?
A. Congenital erythropoietic porphyria
B. Variegate porphyria
C. Porphyria cutanea tarda
D. Acute intermittent porphyria
E. Erythropoietic porphyria
Answer- D- Acute intermittent porphyria; the patient is suffering from acute intermittent porphyria as is evident from the clinical manifestations- the typical combination of abdominal pain, psychiatric symptoms and increased amounts of urinary porphyrins and their precursors.
The Porphyrias are a group of rare metabolic disorders arising from reduced activity of any of the enzymes in the heme biosynthetic pathway. The disorders may be either acquired or inherited through a genetic defect in a gene encoding these enzymes. These deficiencies disrupt normal heme production, and produce symptoms when increased heme is required. Porphyrin precursors, overproduced in response to synthetic pathway blockages, accumulate in the body and cause diverse pathologic changes thereby becoming the basis for diagnostic tests.
The diagnosis of acute porphyria can be confirmed by repeating the quantitation of urinary porphyrin during an acute episode and finding elevated levels (2–5 times of normal) of porphobilinogen.
Acute intermittent porphyria is inherited as an autosomal dominant, though it remains clinically silent in most patients who carry the trait. Clinical illness usually develops in women. Symptoms begin in the teens or 20s, but onset can begin after menopause in rare cases. The disorder is caused by partial deficiency of porphobilinogen deaminase activity, leading to increased excretion of aminolevulinic acid and porphobilinogen in the urine. The diagnosis may be elusive if not specifically considered. The characteristic abdominal pain may be due to abnormalities in autonomic innervations in the gut. In contrast to other forms of porphyria, cutaneous photosensitivity is absent in acute intermittent porphyria. Attacks are precipitated by numerous factors, including drugs and intercurrent infections.
Complete recovery between attacks is usual. Any part of the nervous system may be involved, with evidence for autonomic and peripheral neuropathy. Peripheral neuropathy may be symmetric or asymmetric and mild or profound; in the latter instance, it can even lead to quadriplegia with respiratory paralysis. Other central nervous system manifestations include seizures, psychosis, and abnormalities of the basal ganglia.
The diagnosis can be confirmed by demonstrating an increased amount of porphobilinogen in the urine during an acute attack. Freshly voided urine is of normal color but may turn dark upon standing in light and air.
Avoidance of factors known to precipitate attacks of acute intermittent porphyria—especially drugs can reduce morbidity. Starvation diets also cause attacks and so must be avoided.
Treatment with a high-carbohydrate diet diminishes the number of attacks in some patients. Acute attacks may be life-threatening and require prompt diagnosis, withdrawal of the inciting agent (if possible), and treatment with analgesics and intravenous glucose and hematin. Electrolyte balance requires close attention. Liver transplantation may provide an option for patients with disease poorly controlled by medical therapy.
The steps of heme synthesis and the defects in different porphyria are highlighted in the image-
Figure- Steps of heme biosynthesis
Congenital erythropoietic porphyria occurs due to deficiency of Uroporphyrinogen III synthase. Photosensitivity is the main feature, neurological involvement is no there.
Variegate porphyria occurs as a result of deficiency of Protoporphyrinogen oxidase. Clinical manifestations include photosensitivity, abdominal pain and neuropsychiatric symptoms.
Porphyria cutanea tarda occurs due to deficiency of Uroporphyrinogen decarboxylase enzyme and is manifested by photosensitivity, neurological involvement is absent.
Erythropoietic porphyria is caused due to deficiency of Ferrochelatase enzyme. Clinically it is manifested by cutaneous hypersensitivity.
Since in the given case the patient has mainly neurological symptoms and there is no photosensitivity, hence the porphyria with cutaneous hypersensitivity e.g. congenital erythropoietic porphyria, Variegate, Porphyria cutanea tarda or Erythropoietic porphyria is ruled out.
Thus the only option left is acute intermittent porphyria- option -D
For further reading of Acute intermittent porphyria, follow the link-