False-Positive Accumulation of Metaiodobenzylguanidine in a Case with Acute Intermittent Porphyria

Abstract

We report a 36-year-old woman presenting with hypertensive encephalopathy followed by bulbar palsy and quadriplegia. After an extensive screening for secondary causes of hypertension, the patient was suspected of having pheochromocytoma due to increased levels of catecholamines in the plasma and the urine, and positive 131 I-metaiodobenzylguanidine (MIBG) accumulation in the gallbladder. However, MIBG accumulation was not reproducible without any tumors accompanying this accumulation in the gallbladder. A diagnosis of acute intermittent porphyria was finally confirmed based on the characteristic pictures, increased urinary excretion of porphobilinogen, and identification of a heterozygous missense mutation of R173W in the hydroxymethylbilane synthase gene. This case highlights a pitfall in utilizing MIBG to detect a source of excessive catecholamine and also suggests the importance of having a complete clinical history and extensive work-up of any possible differential diagnosis. We also review the potential mechanism by which falsepositive MIBG accumulation occurs.

Radiopharmaceuticals in Acute Porphyria

“…In the literature search, a case report of a falsepositive accumulation of I-131 iobenguane with acute intermittent porphyria was found. 9 Because this case was not related to porphyrogenicity of the radiopharmaceutical, it was excluded. No other articles were found by using the described key words.…”