A Case of Fishy Smell-Fish Malodor Syndrome

Abstract Introduction: Primary trimethylaminuria (TMAU), also known as fish malodor syndrome is a rare condition that is characterized by trimethylamine excess. The hallmark of this condition is a body malodor similar to decaying fish. As this metabolic disorder is uncommon, this case highlights the management options for an endocrinologist. Case presentation: A 56-year-old man was referred to the endocrine clinic for TMAU. Starting in puberty, the patient’s family and friends noted a malodor that he has never been able to detect. After several decades, the patient was diagnosed clinically by a dermatologist. Since then, the patient’s management had included avoiding cholines in his diet, which included egg yolks and salt-water fish. Additionally, for severe episodes occurring once to twice a year, he took a cup of charcoal daily plus Metronidazole 500 mg twice a day for ten days. The patient was the only member of his family with this condition. Physical exam was unremarkable expect for a faint malodor. Metronidazole, charcoal, and a genetics consult were ordered. Discussion: TMAU is a rare metabolic disorder in which an individual is not able to convert trimethylamine into trimethylamine N-oxide due to a defect in the hepatic oxidase system. It results from a mutation in the flavin-containing monooxygenase 3 gene (FMO3) that is inherited via autosomal recessive pattern. An excess excretion of trimethylamine in the urine, breath, sweat, and reproductive fluids results in a body malodor similar to that of decaying fish. The odor may be exacerbated by increase in body temperature, emotional changes, puberty, and prior to and during menstruation in women and often results in distressing psychosocial difficulties. Thus, early institution of dietary and pharmacological measures will likely have a major impact on quality of life. Treatment options are limited and include topical, dietary, and medications. Topical approaches include antiperspirants, deodorants, and pH-balanced soap. A diet low in choline-containing foods such as dairy, beans, and marine fish is beneficial as choline is metabolized to trimethylamine by the intestinal bacteria. For severe cases, antibiotics such as Metronidazole, Rifaximin, and Neomycin sulfate are helpful to reduce the intestinal bacterial load. Other therapeutic strategies consist of activated charcoal (750 mg twice a day for ten days) and copper chlorphyllin (60 mg three times a day for three weeks); both reduce urinary free trimethylamine and increase the concentration of trimethylamine N-oxide.