Abstract & Commentary
Synopsis: This condition preferentially affects large myelinated fibers of the posterior roots, may respond favorably to treatment, and may be a restricted form of chronic inflammatory demyelinating polyradiculoneuropathy.
Source: Sinnreich M, et al. Neurology. 2004;63:1662-1669.
Sinnreich and colleagues report that patients presenting with ataxic sensory neuropathy and normal nerve conductions may be suffering from chronic immune sensory polyradiculopathy, a variant of chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) that is responsive to immune therapy. The pathology in these patients is localized to the sensory roots, explaining the normal peripheral conduction studies.
Fifteen patients were described. Sensory polyradiculopathy was suspected because of abnormal somatosensory evoked responses, or enlargement of lumbar nerve roots, some with enhancement. CSF protein was elevated in 13/14 patients, as is often seen in CIDP. Three had lumbar sensory root biopsies that showed primary demyelination and endoneurial inflammation. Six of 6 patients, that were treated with immune modulating therapy, had marked improvement in their ambulation.
The diagnosis of CIDP is not unlike that of multiple sclerosis, in that both require demonstration of lesions with demyelination. CIDP is a more difficult diagnosis to make, however, as it relies on electrodiagnostic rather than imaging studies. Sensory conductions, in particular, are notoriously insensitive for detecting demyelination, so that when only the sensory nerves are affected, a sural nerve biopsy may be required to make the diagnosis. Even that, however, may not be sufficient, if the lesions are confined to the sensory roots, as reported in this paper.
Now that Sinnreich et al have established that the entity exists, how does one make a diagnosis of immune sensory polyradiculopathy? Given the insensitivity of current nerve imaging studies, should all patients that present with sensory ataxic neuropathy, abnormal somatosensory responses, and increased CSF protein, have a trial of immune modulating therapy. If so, what therapeutic modalities should one use, and how should improvement be measured? If not, how many potentially treatable patients would be denied therapy? These are important issues, as sensory ataxic neuropathy is relatively common in clinical practice, particularly in the aging population. Perhaps more emphasis should be given to the development of reliable nerve imaging studies, so that the diagnosis of CIDP could becomes as easy to make as that of multiple sclerosis. — Norm Latov
Dr. Latov is a Professor of Neurology and Neuroscience and Director of the Peripheral Neuropathy Center, Weill Medical College of Cornell University.