Ataxia and areflexia in SOAA.

Fifteen patients with the classical syndrome of ophthalmoplegia, ataxia, and tendon areflexia (SOAA) were studied in an attempt to clarify the mechanisms of ataxia and myotatic hyporeflexia. All showed features of cerebellar rather than sensory ataxia. Peripheral nerve conduction studies, including F-waves, were normal in a majority of the patients, as was needle EMG. Low-amplitude compound sensory nerve potentials were seen in four patients only, and mild slowing of sensory conduction velocity in two. Three had abnormal blink reflex studies, suggestive of a central lesion in two, and another two showed a transient delay of N5 peak of brainstem auditory evoked potentials. Somatosensory evoked potentials were normal. Despite clinically depressed or absent tendon jerks, T-waves were elicited at normal latencies. These findings do not support the prevailing view that the neurological abnormalities in SOAA are due to involvement of sensory fibres in the peripheral nerves and dorsal roots. We suggest that lesions scattered in the brainstem tegmentum and in the cerebellar peduncles are responsible for the ataxia and the depressed tendon jerks.