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Exploring Olfactory Function and Its Relation with Behavioral and Cognitive Impairment in Amyotrophic Lateral Sclerosis Patients: A Cross-Sectional Study

Background: Behavioral and cognitive impairment are common in amyotrophic lateral sclerosis (ALS) and represent a continuum with frontotemporal dementia (FTD). Olfactory dysfunction has been described in a subset of ALS patients and might be associated with frontotemporal and insular cortex dysfunction. Objective: To evaluate olfaction dysfunction in ALS patients and its relationship with either cognition or behavioral impairment. Methods: 28 consecutive ALS patients underwent an extensive cognitive and behavioral battery and were classified as patients with normal cognition (ALS-N, n = 11) or with part of the ALS-FTD spectrum (n = 17), including either cognitive or behavioral impairment or dementia. Odor verbal and visual identification and discrimination were investigated in patients and age-matched controls using a test adapted from the Sniffin' Sticks. Results: Olfactory function was significantly different between ALS-FTD spectrum patients and controls (p < 0.001) and inversely correlated with behavioral and cognitive performance. The 10-point cutoff distinguished ALS-N from ALS-FTD spectrum patients with a sensitivity and specificity of 71 and 100%, respectively. Conclusions: Hyposmia is common in a subset of ALS patients and strongly associated with behavioral and cognitive impairment. Olfactory testing may represent an early screening tool in order to identify ALS subjects with cognitive/behavioral dysfunction. Further studies in larger series are mandatory in order to better investigate clinical and pathological aspects in this group of patients.