Assessment of olfaction in multiple sclerosis: evidence of dysfunction by olfactory evoked response and identification tests.

OBJECTIVE To resolve whether the olfactory pathways are affected in multiple sclerosis. METHODS Olfaction was assessed by: (1) The University of Pennsylvania smell identification test (UPSIT, which uses microencapsulated odours that are released when scratched with a pencil) in 72 patients with multiple sclerosis and 96 controls, (2) olfactory evoked potentials (OEP) to 20 ppm H2S by volume, and 50% CO2 in air for 45 patients with multiple sclerosis and 47 controls. The abnormality rate in patients with multiple sclerosis for both tests (1) and (2) was compared with that for visual evoked potentials measured using a standard checquerboard technique. RESULTS By comparison with controls, patients exhibited significantly low scores on the smell identification test with 15% of patients scoring outside the 95% confidence intervals for controls. The UPSIT was occasionally abnormal when the visual evoked potential (VEP) was normal. In general UPSIT scores correlated well with the H2S-evoked response in controls and patients. For H2S, there was a statistically significant increase of latency and decrease of amplitude for patients compared with controls. Increased H2S latency and reduced UPSIT score correlated with greater disability on conventional rating scales. Overall, H2S responses were abnormal in about one quarter of patients with multiple sclerosis. The sensitivity of UPSIT and OEP was similar although disorder on one test did not necessarily indicate abnormality in the other. The visual evoked potential was found to be a more sensitive indicator of disease than OEP or UPSIT. CONCLUSION These findings confirm the existence of olfactory dysfunction in multiple sclerosis and validate a new evoked potential technique.