Can Language Characteristics Contribute to the Classification of Neurodegenerative Disorders? -An Exploratory Study

Objective Evaluating language symptoms is challenging owing to their varied presentations. We developed a Japanese Language Screen (JLS) to assess 11 language aspects, including agrammatism, impairment of articulation and prosody (IAP), word recall, syntactic comprehension, meaning of proverbs, and writing, considering the unique features of the Japanese language. Methods Using the JLS, we assessed the language functions in patients with Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), progressive supranuclear palsy (PSP), and healthy controls (HC) to identify language symptoms specific to each condition and determine whether the JLS can differentiate between diseases and HC. Results The study included 168 participants. The total JLS score categorized the participants' language status as normal or impaired. According to the total score, PSP patients had more severe language deficits than AD patients, despite comparable cognitive scores. Substantial differences were found in the 11 assessed items for each disease. Patients with AD and PSP showed decreased performance in more than half of the items compared to HC, with the PSP group being more impaired. ALS patients showed decreases in IAP and writing, notably in the meaning of proverbs, whereas PD was closely comparable to HC. Conclusion This study suggests that while the JLS is useful for understanding the language symptoms associated with neurodegenerative disorders, its ability to classify them remains limited.