As mentioned earlier, a small proportion of cases began as acute GBS but continue to progress or relapse in the following months (Gorson et al, 1997). Another comprehensive account of the disease have been given by Hughes and associates. All of these studies have included cases with clinical progression for longer than 8 or 12 weeks; thus CIDP has come to be defined in part by a progressive polyneuropathy of this duration.
As might be imagined from the experience with GBS, there are variant syndromes that align with CIDP but have special clinical characteristics. The best characterized of these is multifocal conduction block (called multifocal acquired demyelinating sensory and motor neuropathy, or MADSAM). Also described is a polyradicular process that presents as an ataxic illness with large fiber attributable sensory loss and spared sensory nerve action potentials (see Sinnreich et al), and a slowly progressive distal neuropathy (distal acquired demyelinating symmetrical neuropathy; DADS). In the latter, there are distal sensory and sometimes motor, disturbances and greatly prolonged distal latencies in most patients, and two-thirds have an associated IgM monoclonal gammopathy with kappa light chain component; the illness responds poorly to treatment, aligning it clinically in some respects with the anti-MAG neuropathies but in most clinical and electrophysiologic features appearing to be a variant of CIDP (see Katz et al).
The status of a predominantly axonal polyneuropathy that clinically simulates CIDP and responds to some extent to the same immunomodulating treatments has been described by Uncini and colleagues and by Gorson and Ropper. The present authors have the impression that it is an immune-mediated neuropathy comparable to CIDP but with preferential destruction of axons rather than of myelin. Its frequency as a cause of acquired polyneuropathy is unknown, but we see several new cases every year.
Also recognized is the frequency (up to 25 percent of the patients in some series, less often in our experience) with which there was a parallel systemic condition such as paraproteinemia, lymphoma, an undifferentiated reactive adenopathy or lupus, in association with an inflammatory demyelinating polyneuropathy (even aside from the rare DADS process mentioned above). These associations create problems in nosology that can be reconciled by labeling a given instance as, for example, “CIDP with paraproteinemia” or “CIDP with lupus,” thus separating such cases from the idiopathic variety but the distinctions are tenuous. These symptomatic inflammatory polyneuropathies respond to corticosteroids, albeit unpredictably, and to treatment of the underlying disease.
Laboratory features The CSF protein is elevated in more than 80 percent of patients with CIDP, typically in the range of 75 to 250 mg/dL. In rare instances there is papilledema and a pseudotumor cerebri syndrome (see Chap. 29) in relation to extremely high levels of CSF protein (usually >1,000 mg/dL). Elevation of the CSF gamma globulin fraction and a mild lymphocytic pleocytosis are found in 10 percent of patients (often in those who are HIV-seropositive), a considerably higher percentage than in our series.