Abstract:
Abstract
Background: A unique syndrome affecting young adults of unexplained hearing loss often
associated with uncorrectable poor visual acuity and lower extremity numbness is endemic in Dar
es Salaam. This study characterized the hearing loss, associated it with other symptoms, and
gathered information on potential causes.
Methods: Forty-seven patients (23 men, 24 women) <40 years old with a symptom consistent
with the syndrome, negative syphilis test, and no head injury history were recruited from
Muhimbili National Hospital. 18 controls (10 men, 8 women) were recruited from the same
neighborhoods as patients. Hearing ability and cochlear outer hair cell function (distortion-product
otoacoustic emissions (DPOAEs)) were assessed, as were visual acuity and color vision.
Peripheral neuropathy was evaluated using the Michigan Neuropathy Screening Instrument
(MNSI), and physical examination. Blood C-reactive protein levels and toenail trace metal
concentrations were measured. Environmental exposures were elicited using a questionnaire.
Patients with at least two of the following signs were defined as having the syndrome: poor
hearing with normal DPOAEs, vision not correctable to better than 20/30, or a MNSI score greater
than 4.
Results: 29 participants met the case definition. CRP levels did not differ between groups but
manganese, cobalt and tin levels were each greater in the cases than controls. No other
environmental exposure differences were noted.
Conclusions: Toenail manganese, cobalt, and tin levels were higher in those with the syndrome.
These metals are potential neurotoxins suggesting a possible environmental origin for this unique
and debilitating syndrome
