A case series of PLS patients with frontotemporal dementia and overview of the literature

Objective: Primary lateral sclerosis (PLS) is a rare form of motor neuron disease characterised by UMN degeneration leading to slowly progressive spasticity. Whether it is a separate disease or a subtype of ALS has been debated. In ALS comorbid frontotemporal dementia (FTD) is frequently seen (±15%). However, cognitive and behavioural changes are generally not considered to be a part of PLS. Methods: To report the clinical findings and frequency of PLS patients that developed FTD in a referral-based cohort and provide an overview of the literature. Results: In our cohort six out of 181 (3.3%) PLS patients developed FTD. In the literature a few cases of PLS with FTD have been reported and only a limited number of small studies have investigated cognition in PLS. However, when these studies are summarised a pattern emerges with FTD diagnoses in ±2% and frontotemporal impairment in 22% of patients. Conclusions: These findings suggest that PLS is part of the FTD-MND continuum and would favour viewing it as a subtype of ALS. It is, however, not a restricted (isolated UMN involvement) phenotype.