Acute intermittent porphyria (AIP) is an autosomal dominant disease due to deficient Porphobilinogen (PBG) deaminase activity. Hyponatremia, found in approximately 20% of symptomatic AIP, is often due to inappropriate ADH secretion (SIADH). An association between AIP and hyperthyroidism is not clearly established. We describe a patient with AIP and SIADH who presented with Graves hyperthyroidism. A 35-year-old lady was admitted with lower abdominal pain. Physical examination was normal apart from sinus tachycardia and small diffuse goitre. Laboratory investigation demonstrated hyponatremia (serum Na 120 meq/l) and hyperthyroidism. Laparoscopy was normal. Abdominal pain resolved and hyponatremia improved over the next few days and she was treated with Carbimazole 20 mg bd. Eight weeks later, she was re-admitted with abdominal pain, nausea and vomiting. Physical examination was unremarkable and she was biochemically euthyroid on carbimazole 15 mg daily. Following metoclopramide and diclofenac treatment, she became hyponatremic (serum Na 120 meq/l) and quadriparetic with respiratory muscle weakness. SIADH was found to be the cause of hyponatremia. The combination of SIADH and recurrent abdominal pain led to the diagnosis of AIP, confirmed by the presence of elevated urinary PBG and total porphyrin and reduced Red Blood Cell PBG deaminase activity. Family screening showed that father and sister were affected. Following withdrawal of diclofenac and metoclopramide and treatment with IV 20% dextrose, a marked improvement occurred with resolution of muscle weakness and hyponatremia. Four years later, following outpatient radioiodine therapy, she is euthyroid with no further exacerbation of AIP. The sequence of events described here and in two previous reports supports an association between AIP and hyperthyroidism. Hyperthyroidism may provoke and/or prolong an episode of AIP, possibly by increasing hepatic 5-aminoclavulinate (ALA) synthase activity.
07 - 09 Nov 2005
Society for Endocrinology