Distinctive Olfactory Pattern in Parkinson's Disease and Non-Neurodegenerative Causes of Hyposmia

Olfactory dysfunction is common in Parkinson's disease (PD). The characteristics of the hyposmia in PD have not been well defined.

To characterize the pattern of the olfactory deficit in PD and in other non-neurodegenerative aetiologies of hyposmia.

We evaluated 36 PD patients, 20 patients with hyposmia secondary to acute respiratory infection (ARI), and 19 patients with hyposmia secondary to traumatic brain injury (TBI). For comparison purposes, we included a group of 15 controls age and sex matched with PD patients. PD patients were classified based on disease duration and severity in de novo PD, and PD with and without chronic levodopa-related complications. The Barcelona Smell Identification Test was applied to all participants.

For the first cranial nerve odours, PD patients scored lower than controls on smell detection (85.28 vs. 97.67%, p = 0.006), definition (79.58 vs. 93.33%, p = 0.007), recognition (63.33 vs. 81%, p = 0.020), and forced choice (58.06 vs. 82%, p < 0.001). Compared with ARI, forced choice was significantly better in PD patients (p < 0.001), but no differences were found regarding other olfactory characteristics. TBI patients showed significantly lower scores than the other study groups in all the olfaction items. For the fifth cranial nerve odours, recognition (p = 0.003) and identification (p = 0.019) were lower in the TBI group than in the others. No differences were found among PD subgroups regarding any olfactory characteristic.

A differential pattern of hyposmia was observed in PD patients compared to other non-neurodegenerative aetiologies. Further studies with larger samples should replicate our results.