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.

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