Olfactory bulb changes fall short as imaging marker for PD

By Eleanor McDermid, Senior medwireNews Reporter

Functional and histopathological changes in the olfactory bulb in patients with Parkinson’s disease (PD) do not equate to a volume change that is detectable on magnetic resonance imaging (MRI), say researchers.

Olfactory function is often impaired in PD patients, and previous studies suggest that olfactory function is associated with olfactory bulb volume.

This was the case in the 31 healthy control participants of the current study, in whom composite scores on the Sniffin’ Sticks test battery, as well as scores in the discrimination subdomain, were significantly associated with olfactory bulb volume on MRI.

The association with odour discrimination remained significant after adjustment for multiple correlations, report Karsten Witt (University Hospital Schleswig-Holstein, Kiel, Germany) and co-researchers in the European Journal of Neurology.

But there was no such association in 52 patients with PD, despite 10 being classed as anosmic (composite score <16) and 35 as hyposmic (composite score <31). None of the controls were anosmic, but eight were hyposmic. Olfactory bulb volume also did not correlate with disease duration or Unified Parkinson’s Disease Rating Scale score.

Average olfactory bulb volumes were not significantly different between the groups, at 41.5 mm³ for the left and 42.1 mm³ for the right in PD patients, and corresponding values of 41.0 and 46.6 mm³ in controls.

The researchers say the lack of association between olfactory bulb volume and olfactory function suggests the existence of “volume-independent” olfactory dysfunction in PD patients.

Therefore, MRI “seems not to be an adequate tool to support the diagnosis” of PD, they conclude.

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