Initial Cerebellar Ataxia in Hereditary Adult-Onset Primary Lateral Sclerosis.

Cerebellar ataxia preceding the apparition of primary lateral sclerosis (PLS) is reported herein. Three individuals from 2 independent kindreds experienced ataxia before developing clinical signs of PLS. Disease onset was during the sixth decade or later, and an insidious onset, with progression exceeding 11 years, was observed. Pathochrony was homogenous, consisting of initial gait instability, followed by hand dysmetria 2 years later. During a 5-year follow-up, cerebellar ataxia remained the sole clinical manifestation, preceding the appearance of muscle stiffness, which progressed to a paraparesis, and then to a purely spastic quadriparesis, over 4 years; pseudobulbar dysarthria and dysphagia appeared later. At this disease stage, limb spasticity, hyperactive jaw and limb stretch reflexes, extensor plantar responses, and a spastic dysarthria were found on examination; limb dysmetria and an ataxo-spastic gait were also found. No muscle atrophy or fasciculation was observed. Among ancillary tests, electromyographic studies performed 6 years after disease onset revealed normal motor unit action potentials and absence of spontaneous activity, in 2 individuals. MRI revealed normal cerebellum and brainstem in 2 cases. Inheritance was dominant in both kindreds, and extensive genetic testing was negative. It is concluded that cerebellar ataxia preceded the appearance of a purely spastic spinobulbar syndrome (which fulfilled the clinical diagnostic criteria for PLS) during a 5-year period in 3 patients with a hereditary, adult-onset form of PLS; subsequent disease progression was equivalent to that of sporadic PLS. Further studies are needed to fully delineate the clinical and genetic spectra of adult-onset PLS.