Background. Motor neuron disease (MND) patients can show oral language deficits mimicking those of frontotemporal degeneration (FTD). Although dysgraphic features have also been reported within the MND-FTD continuum, their characteristics and clinical relevance are still largely unexplored.
Aims. Profiling writing disorders in MND patients can help further define their cognitive semiology and thus convey relevant clinical entailments. Therefore, this study aimed at reviewing evidence of writing impairment in MND patients. This review was implemented and reported by consulting Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Qualitative/quantitative measures of writing abilities in MND patients were the primary outcome. Both group studies and case reports/series were taken into consideration. Twenty contributions were included out of an initial N = 83. Potential biases in generalizing results were qualitatively controlled for by extracting background, disease-related, neuropsychological, and neuroanatomofunctional secondary outcomes.
Main Contribution. Fifteen studies assessed writing abilities in Japanese patients, whereas the remaining eight in western patients. Central dysgraphic features were reported in both neuropsychologically impaired and unimpaired MND patients. Non-phonologically plausible and morpho-syntactic errors were frequently reported. Although FTD was frequently co-occurent, neither cognitive nor language impairment fully accounted for writing impairment in some patients. By contrast, evidence of peripheral dysgraphia was scarce. Patients displaying writing deficits often presented with bulbar signs and perisylvian cortex involvement (including Exner’s area and the left angular gyrus). Writing deficits proved to be associated with abnormalities in executive functioning and its neural substrates. Writing-to-dictation tasks as well as writing samples assessment proved to be useful to detect writing errors.
Conclusions. Dysgraphic features in MND patients might be due to dysfunctions of the graphemic buffer. The lexico-semantic route appeared to be less involved. However, a mixed peripheral/central involvement cannot be ruled out. In this population, executive/attentive deficits are likely to contribute to writing errors as well. Writing deficits might thus be specific of MND patients’ cognitive/language impairment profiles. The evaluation of writing abilities via writing-to-dictation/narrative writing tasks may be useful when assessing cognition/language in both neuropsychological-impaired and -unimpaired MND patients – especially when severe dysarthria/anarthria is present and prevents clinicians from assessing oral language.