Your nose is the scenter of your face

PLoS One. 2017 Jan 20;12(1):e0170492. doi: 10.1371/journal.pone.0170492. eCollection 2017.

Longitudinal Testing of Olfactory and Gustatory Function in Patients with Multiple Sclerosis. Uecker FC, Olze H, Kunte H, Gerz C, Göktas Ö, Harms L, Schmidt FA

The aim of the study was to investigate changes of the olfactory and gustatory capacity in patients with multiple sclerosis (MS).

20 MS patients were tested longitudinally for 3 years after initial testing. The Threshold Discrimination Identification test (TDI) was used for subjective olfactometry. Objective olfactometry was performed by registering olfactory evoked potentials (OEP) by EEG. The Taste Strip Test (TST) was used for gustatory testing.

45% of the patients showed olfactory dysfunction in the follow-up TDI test and 50% showed delayed OEP´s. 20% of the patients showed gustatory dysfunction on follow-up visit. The patients showed mild disease activity with 0,3 ± 0,5 relapses over the testing period and no significant change of their olfactory and gustatory capacity. The olfactory capacity for the discrimination of odors correlated inversely with the number of relapses (r = -0.5, p ≤ 0.05). The patients were aware of their olfactory deficit.

Olfactory and gustatory dysfunction is a symptom in MS patients and may be a useful parameter to estimate disease progression in MS patients. As the discrimination of odors is processed in higher central regions of the central nervous system (CNS), the results suggest that olfactory dysfunction could be due to CNS damage.

I'd be lying if I said I didn't wear perfume; admittedly it's one of my vanities, having spent most of my formative years searching for that signature perfume. What if you couldn't smell? Your sense of smell also allows you to taste. Dysfunction in smell is commonly featured in Parkinson's disease and Alzheimer's disease, preceding the development of clinical symptoms by a number of years. And not surprisingly, it would appear MS has also joined the list. Studies have reported rates of 11-41% in MS.

Here, Uecker et al. research whether there is a link with disease evolution over 3y. Undoubtedly, their sample size leaves a lot to be desired with a high drop out, but they report smell dysfunction in 10/20 subjects at the start of the study! This figure didn't change much over the 3y if you compensate for the drop outs and their disability did not alter either over the study period (70% of subjects being on treatment may have had something to do with this!). They also noted that 3/4 expressing difficulty with taste also had smell problems.

The more interesting question is why does it occur in MS in the first place? The authors point out that olfactory bulb/tract (smell organ) and adjacent inferior frontal cortex (front of the brain) is demyelinated in ~70% of MS cases confirmed at autopsy.

Testing this may not be that informative as far as disease activity is concerned, but it still has wider implications for management. Food for thought!

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