Syndrome of inappropriate antidiuretic hormone secretion associated with coproporphyria: case report and review of literature.

OBJECTIVE: To remind physicians to consider the hepatic porphyrias in the differential diagnosis of the syndrome of inappropriate antidiuretic hormone secretion. METHODS: We present a case report of a patient seen in the hospital for severe hyponatremia, who was discovered to have the syndrome of inappropriate antidiuretic hormone secretion attributable to coproporphyria. Results of laboratory tests of the patient and her family are presented. RESULTS: A 54-year-old woman was seen in the hospital because of severe hyponatremia accompanied by generalized seizures. Her serum sodium concentration was 112 mEq/L, with concomitant serum and urine osmolalities of 235 and 639 mOsm/kg, respectively. Renal, thyroid, and adrenal functions were normal. Brain, chest, abdominal, and pelvic imaging studies were negative for occult malignant disease. Urinary excretions of porphobilinogen and aminolevulinic acid were substantially elevated. Results of follow-up urine, plasma, and fecal porphyrin studies were consistent with coproporphyria. Results of porphyrin metabolic studies of the patient's family showed normal findings in her parents and a minimally increased fecal coproporphyrin concentration and urinary uroporphyrin excretion in her sister. CONCLUSION: An endocrinology consultation is often requested for patients with hyponatremia. It is important to consider the acute hepatic porphyrias in the differential diagnosis, even though these are rare disorders and the family history may not always be helpful because of the high frequency of asymptomatic carriers.