Sensory neuronopathy

Clinical features
The term neuronopathy was introduced to describe a neurological syndrome characterized by primary damage of the nerve cell body (figure).

Figure: Dorsal root ganglia of a patient with sensory neuronopathy and anti-Hu antibodies. There is widespread loss of sensory neurons replaced by proliferation of satellite cells. Hematoxylin-eosin x10.

A paraneoplastic origin is one of the causes of sensory neuronopathy. The most common associated tumor is small-cell lung carcinoma. The main clinical complains at the onset are pain and paresthesias with asymmetric distribution that involve arms rather than the legs. Later, pain is replaced by numbness, limb ataxia, and psedoathetotic movements of the hands. The neurologic examination shows abolition of the deep tendon reflexes and involvement of all modalities of sensation but with clear predominance of the joint position and vibratory senses. Thirty percent of the patients complaint of uni or bilateral numbness on the face due to trigeminal ganglia damage. Sensorineural deafness and sensory deficits in the trunk are less usual. The typical sensory neuronopathy has a subacute onset and progresses rapidly to involve the four limbs and then may stabilize although, by the time its does so (6-9 months), the patient may be confined to bed or chair due to ataxia. In 10% of the patients, the neuropathy runs a mild, very slowly clinical evolution. These patients may remain ambulatory and with an independent life for years in absence of any antitumoral or immunosupresive treatment. Paraneoplastic sensory neuronopathy is not always an isolated syndrome and the neurological evaluation may demonstrate involvement of the motor nerves, peripheral autonomic nervous system, or different areas of the brain (encephalomyelitis). Electrophysiologic studies that show marked, but not restricted, involvement of the sensory fibres with absent sensory nerve action potentials in at least one of the nerves studied. The CSF may show mild lymphocitic pleocytosis. Sural nerve biopsies show fiber loss without features of regeneration or demyelination. Perivascular inflammatory infiltrates without necrosis of the vessel walls may be observed in the epineural vessels.

Associated antibodies

Most of the patients with sensory neuronopathy present anti-Hu antibodies. Other antibodies less frequently associated are anti-CV2(CRMP5) and anti-amphiphysin.

Treatment
As in other paraneoplastic neurological syndromes associated with neuronal damage, sensory neuronopathy rarely improves with treatment. The best chance to at least stabilize the syndrome is to induce a complete response of the tumor. Immunotherapy rarely is effective but a trial with intravenous immunoglobulins, steroids or plasmapheresis is indicated because there are a few patient who improved.

Selected references
1. Camdessanché JP, Antoine JC, Honnorat J, et al. Paraneoplastic peripheral neuropathy associated with anti-Hu antibodies. A clinical and electrophysiological study of 20 patients. Brain 2002;125:166-75.
2. Chalk CH, Windebank AJ, Kimmel DW, et al. The distinctive clinical features of paraneoplastic sensory neuronopathy. Can J Neurol Sci 1992;19:346-51

3. Graus F, Bonaventura I, Uchuya M, et al. Indolent anti-Hu-associated paraneoplastic sensory neuropathy. Neurology 1994; 44: 2258-61.

4. Graus F, Keime-Guibert F, Reñé R, et al. Anti-Hu-associated paraneoplastic encephalomyelitis: analysis of 200 patients. Brain 2001;124:1138-48.
5. Keime-Guibert F, Graus F, Fleury A, et al. Treatment of paraneoplastic neurological syndromes with antineuronal antibodies (anti-Hu, anti-Yo) with a combination of immunoglobulins, cyclophosphamide, and methylprednisolone. J Neurol Neurosurg Psychiatry 2000; 68: 479-82.

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