In addition to the subacute pansensory syndrome described previously and paraneoplastic, postinfectious, and toxic processes, there is a yet another more chronic idiopathic syndrome characterized by severe global sensory loss and ataxia. We have encountered several such patients resembling the cases described by Dalakas. The numbness and sensory findings progressed over months and spread to proximal parts of the arms and legs and then to the trunk. The face and top of the scalp were finally involved. Despite ataxia and complete areflexia, muscular power remained normal and pain was not a problem. There are reports of fasciculations in a few patients, but not in the ones we have seen. Within a year, most of these patients became completely disabled from the ataxia, unable to walk or even feed themselves. Autonomic failure was another feature in a few and one of our patients became deaf. Extensive examinations for an occult cancer, paraproteinemia, Sjögren disease, Refsum disease, autoimmune diseases, and all potential causes of an ataxic neuropathy proved to be frustratingly negative. Of course, it is possible that some patients had an as yet undiscovered tumor. Yet other instances have had all the features of a truncal–limb sensory neuropathy, with little or no ataxia and only muted reflexes; these have had a more benign course but still no cause was found (Romero et al). Illa and colleagues (2001), in a review of 17 patients with idiopathic sensory ataxic neuropathy, found antibodies against the ganglioside GD1 in only 1 case and concluded that the majority was not caused by an immunologic mechanism.
The motor nerve conduction studies have been normal or slightly impaired, while the sensory potentials were eventually lost (but they may at first be normal). A puzzling feature in 2 patients has been an unexpected preservation of many sensory nerve potentials even after a year of illness. In these cases, the process presumably lay in the dorsal roots rather than in the ganglia. In a few instances the MRI has shown a change in the posterior columns of the spinal cord, certainly as a secondary phenomenon from the spinal nerve and root disease. The spinal fluid has generally contained a slightly elevated protein concentration with few or no cells, up to 18/mm3 in our cases.
Pathologic examination of the sensory ganglia in a few cases has disclosed an inflammatory process identical to that of Sjögren disease. Our attempts at treatment using plasma exchanges, IVIg, corticosteroids, and immunosuppressive agents have been mostly unsuccessful.
Also mentioned here is a subacute or chronic idiopathic small-fiber ganglionopathy that affects function primarily. These patients complain of pain and burning in proximal body parts, including the face, tongue, and scalp with reduced sensation of pinprick in affected areas. The reflexes may be preserved and vibration sensory perception may be preserved. Our experience with such patients and anecdotal responses to treatment was summarized by Gorson and colleagues (2008). Whether such aberrant proximal sensory complaints as “burning mouth syndrome” (see Chap. 9) are allied with this entity is not clear but they may occur together.
Under this term is collected a group of subacute and chronic dysautonomias that on extensive evaluation cannot be attributed to diabetes, amyloidosis, autoimmune disease, Fabry disease, HIV, toxin exposure, or another systemic disease. A few cases will be found to be due to one of several rare mutations in genes, of which four sites have been described so far (SPTLC1, HSN2, IKBKAP, NTRK1).
A number of such cases, almost half in the series of Suarez and colleagues (1994), have been acute in onset and conform most closely to the “pure pandysautonomia” condition described by Young and colleagues, discussed earlier as a variant of Guillain-Barré syndrome. The others follow a subacute or chronic course and about one-fourth of these have a serum antibody that is directed against the acetylcholine receptor of sensory ganglia (Klein et al).