Abstract
Background/Objectives Sensory processing deficits are common across the FTD-MND spectrum and occur as a consequence of the neurodegenerative disease process. Olfaction is of particular interest, demonstrating potential clinical utility as a biomarker of disease progression. As yet, the underlying mechanisms for disordered sensory processing remain poorly understood in FTD-MND.
Methods In total, 61 participants patients were recruited to this study to determine smell function and the relationship to abnormal smell perception in FTD-MND. In addition to standard diagnostic assessments all participants underwent blood sampling for C9orf72 repeat expansion. All participants completed the 12-item Brief Smell Identification Test and a questionnaire of anomalous smell perceptions.
Results As expected, patients were more impaired in smell function compared to controls (p<0.05), with a spectrum of scores emerging across disease groups; patients with FTD-MND and FTD had poorest smell function (M=7.0 and M=7.83 respectively), compared to MND and controls (M=9.54, and M=0.63 respectively; all p<0.05). A negative correlation was identified between smell score and cognitive functioning (p<0.001).
A distinct pattern emerged within the C9orf72 expansion cohort; patients were more likely to experience anomalous smell perceptions (p<0.01) and there was a negative association between abnormal smell function and abnormal smell perception, with increasing scores of perceptual severity associated with decreasing scores in function (all p<0.05).
Conclusion/Discussion While a spectrum of disordered smell function exists in FTD-MND disease, patients with the C9orf72 expansion have increased vulnerability to experience anomalous perceptions of smell that may be selectively related to impaired sensory functioning coupled with disordered cognition.
