Primary lateral sclerosis (PLS) is an idiopathic non-familial neurodegenerative disorder of upper motor neurones. It presents as a slowly progressive pyramidal tract syndrome, sometimes with marked pseudobulbar symptoms.

The diagnosis is based on exclusion of other causes. Pringle and colleagues¹ proposed diagnostic criteria in 1992 for PLS: adult onset; negative family history; duration of at least three years (to exclude motor neurone disease (ALS)); and normal blood, CSF, EMG, and MRI results. However, it remains an enigmatic, heterogeneous syndrome of uncertain nosology, for some clinically …