Trimethylaminuria Presenting as Persistent Malodor in an Adolescent Female: A Case Report

Abstract Background Trimethylaminuria is a rare metabolic disorder caused by impaired hepatic oxidation of trimethylamine due to deficiency of flavin-containing monooxygenase 3 (FMO3). It leads to accumulation of trimethylamine, resulting in a characteristic fish-like body odor. Although medically benign, it is associated with significant psychosocial distress and frequent misdiagnosis. Case presentation We report the case of a 19-year-old female university student who presented with a three-year history of persistent fish-like body odor beginning shortly after menarche. The odor was continuous, socially noticeable, and worsened with sweating, physical activity, and menstruation. Despite strict personal hygiene measures, including frequent bathing and use of deodorants, there was no improvement. Physical examination was unremarkable except for a noticeable odor. Routine laboratory investigations were normal. Metabolic evaluation revealed elevated urinary trimethylamine with a reduced trimethylamine N-oxide ratio, consistent with impaired TMA metabolism. A diagnosis of trimethylaminuria was made. The patient was managed with dietary restriction of trimethylamine precursors, short-course antibiotics, activated charcoal, and psychological support. Conclusion This case highlights the importance of considering trimethylaminuria in patients presenting with persistent unexplained body odor, particularly when onset occurs around puberty and is resistant to hygiene measures. Early recognition is essential to reduce diagnostic delay and psychosocial burden.