Language impairment in motor neuron disease phenotypes different from classical amyotrophic lateral sclerosis: a review

Up to 35–40% of patients with amyotrophic lateral sclerosis (ALS) present with language deficits falling within the spectrum of frontotemporal lobar degeneration (FTLD). It is currently debated whether frontotemporal involvement occurs or not in motor neuron disease (MND) phenotypes that differ from classical ALS (i.e., both different-from-ALS MNDs and non-classical ALS endo-phenotypes)–this stance being supported by the notion of a common pathology underlying MNDs. To investigate whether language dysfunctions also occur in patients with different-from-classical-ALS adult-onset MNDs can; a) help determine whether the MND-FTLD continuum could be broadened at a neuropsychological level; b) convey relevant entailments to cognitive diagnostics in these populations. The present study thus aimed at reviewing evidence regarding language impairment in different-from-classical-ALS MND patients. Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines were consulted to implement and report the present review. Studies were included if a) language was quantitatively assessed b) in patients diagnosed with different-from-classical-ALS MND phenotypes. Studies assessing demented patients only were excluded. From an original N = 1117 contributions, N = 20 group studies were finally included. Secondary outcomes were taken into account for qualitatively assessing potential biases in generalizing results. Studies were divided into those assessing predominant/pure-upper vs. -lower MND patients (UMND/LMND). Language dysfunctions appeared to be more prevalent and severe in UMND patients. Language screeners were able to detect language deficits in both groups. Lexical-semantic deficits appeared to be highly prevalent in both groups and a selective difficulty in action- vs. object-naming was not infrequently detected. Morpho-syntactic deficits were seldom reported in both groups. Phonological deficits and central dysgraphic features were found in UMND patients only. Patients with different-from-classical-ALS MND phenotypes display language deficits similar to those of classical ALS patients (as far as both prevalence and type are concerned) and thus could be validly included in the MND-FTLD continuum at a neuropsychological level. A greater cortical involvement might account for language deficits being more severe in UMND patients. Consistently with guidelines for cognitive assessment in ALS patients, action-naming tasks might represent a valid and sensitive tool for assessing language in UMND/LMND patients too.