Normal tendon reflexes despite absent sensory nerve action potentials in CANVAS: a neurophysiological study

Area of Science:

• Neuroscience
• Neurology
• Genetics

Background:

• Cerebellar Ataxia with Neuropathy and Vestibular Areflexia Syndrome (CANVAS) is a progressive neurological disorder.
• It involves degeneration of sensory and cerebellar pathways, leading to ataxia and sensory loss.
• Previously, it was thought that all patients with CANVAS lose all sensory nerve function, including reflexes.

Purpose of the Study:

• To investigate the clinical and electrophysiological findings in CANVAS patients with preserved tendon reflexes.
• To determine if specific types of sensory afferents are differentially affected in CANVAS.
• To clarify the diagnostic criteria for large fiber peripheral neuropathy in CANVAS.

Main Methods:

• Clinical examination of 5 CANVAS patients with absent sensory nerve action potentials.
• Assessment of Achilles tendon reflexes and H reflexes in upper and lower limbs.
• Electrophysiological studies to evaluate nerve function.

Main Results:

• All studied CANVAS patients had absent sensory nerve action potentials.
• Despite nerve damage, 5 patients had intact or brisk Achilles tendon reflexes.
• Four patients also showed preserved H reflexes in both upper and lower limbs.

Conclusions:

• Dorsal root ganglion neurons innervating cutaneous afferents are more vulnerable in CANVAS than those innervating muscle afferents.
• Preservation of the Achilles tendon jerk does not rule out a large fiber peripheral neuropathy in CANVAS.
• These findings refine the understanding of CANVAS pathophysiology and diagnostic considerations.