Objective: To investigate olfactory dysfunction (OD) in individuals with Huntington disease (HD) and its relation to disease severity.

Background: HD is a hereditary neurodegenerative disease characterized by a motor and nonmotor symptoms. [1] OD is one of the nonmotor symptoms that may appear early during the disease. Animal studies and post-mortem pathology have shown disease-specific protein aggregation in the olfactory bulb of patients with neurodegenerative diseases. [2] However, the significance of OD and its association with disease progression is not fully defined.

Method: Between June 2021 and March 2022, we recruited patients aged 18 – 75 years with genetic or clinical diagnosis of HD who were referred to UTHealth HDSA Center of Excellence. Evaluations included: the Montreal Cognitive Assessment (MoCA), Unified Huntington’s Disease Rating Scale (UHDRS) subscales, including Total Motor Score (TMS), Total Functional Capacity (TFC), Functional Assessment Scale (FAS), Independence Scale (IS), and Symbol Digit Modalities Test (SDMT). Olfactory function was evaluated by a 12-item Brief Smell Identification Test (B-SIT), a cut-off of <9 was used for abnormal olfactory function.

Results: We recruited a total of 20 patients with a mean age of 51.8 (±12.3) years and a female/male ratio of 1:1. Seventeen patients were white, two were African-American, and one was Indian. Mean CAG repeat length was 44 (±4.8) in those who had genetic test (n=14). Nine patients with stage I HD (TFC 11-13) had a mean TMS of 24.1 (±12.7), SDMT of 40.6 (±12.1), FAS of 24.2 (±1.1), IS of 97.2% (±4.4), MoCA of 26.8 (±2.5), and B-SIT score of 8.3 (±2.4). The mean values for 9 patients with stage II HD (TFC 7-10) were 37.6 (±9.8) for TMS, 23.3 (±7.8) for SDMT, 17.8 (±4.5) for FAS, 80.6% (± 10.4) for IS, 21.3 (±2.5) for MoCA, and 5.9 (±1.4) for B-SIT. Two patients with stage III HD (TFC 3-6) had a mean TMS of 48 (±8.5), SDMT of 18.5 (±3.5), FAS of 19 (±4.2), IS of 65% (±7.1), MoCA of 19.5 (±0.7), and B-SIT score of 3.5 (±0.7).

Conclusion: Our preliminary findings show that OD is present even in early-stage HD and declines with increasing disease severity. We successfully applied the B-SIT and a comprehensive battery in a diverse patient population with plans for inclusion of healthy controls and additional participants with HD. Further studies are warranted to determine the utility of OD as a clinical biomarker in HD.

References: 1. McColgan, P., & Tabrizi, S. (2018). Huntington’s disease: a clinical review. Eur J Neurol, 25(1), 24–34. https://doi.org/10.1111/ene.13413
2. Patino, J et al. (2021). Olfactory Dysfunction in Huntington’s Disease. 1 Jan. 2021: 413–422.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/olfactory-dysfunction-in-patients-with-huntington-disease/