To describe an acute form of pure sensory, presumably immune-mediated, demyelinating polyradiculopathy and to propose the term acute immune sensory polyradiculopathy (AISP).

Chronic immune sensory polyradiculopathy (CISP) is a dysimmune neuropathy affecting preganglionic segments of peripheral sensory nerve fibers characterized by progressive sensory ataxia, and laboratory, radiological and histopathologic evidence of inflammatory demyelination limited to sensory nerve rootlets. Given the preganglionic involvement, routine nerve conduction studies (NCS) are typically normal which obscures the diagnosis. Acute forms have not been described.

A 19 year-old man developed numbness and tingling in all limbs, gait imbalance and incoordination over 3 weeks preceded by a self-limited episode of headache and fever. He had normal muscle strength, sensory deficits to all modalities extending to upper arms and thighs, limb and gait ataxia and globally absent/reduced reflexes.

NCS/EMG were normal. Cerebrospinal fluid revealed 1 cell/mm³ and protein of 94 mg/dL. Brain and entire spine MRI with/without gadolinium were unremarkable. Somatosensory evoked potentials (SEP) demonstrated poorly formed, dispersed cervical and cortical responses with median and tibial stimulation. The patient was started on intravenous immunoglobulin (IVIG). One month later the median cervical and cortical absolute and interpeak latencies were prolonged; routine NCS/EMG remained normal. Weekly IVIG resulted in clinical recovery and normalization of SEP abnormalities. Interval increased amplitude of a persistently normal medial plantar response raises the possibility of a much milder postganglionic involvement.

In patients presenting with acute, diffuse sensory symptoms and imbalance with normal NCS/EMG and imaging studies, the diagnosis can be challenging and AISP should be considered. Altered morphology and prolongation of SEP responses at the root level may be the only finding indicative of nerve root demyelination. Elevated CSF protein can assist in the diagnosis. A preceding viral illness and positive response to IVIG suggests that AISP is in the spectrum of Guillain-Barré syndrome.