An antecedent infection is usually not identified in patients with CIDP as it is in GBS. Furthermore, CIDP may be distinct immunologically from GBS, insofar as certain HLA antigens occur with greater frequency in patients with CIDP than they do in the normal population, whereas there are no clear HLA propensities in patients with GBS. Finally, in contrast to acute GBS, many cases of CIDP respond favorably to the administration of prednisone. An ambiguity is introduced here because, as mentioned in the section on GBS, Hughes et al (1992) has described a group of patients with polyneuritis in whom weakness progressed steadily for 4 to 12 weeks and who responded to corticosteroids (subacute GBS), in such cases, blurring the distinction between GBS and CIDP.
Chronic symmetric sensorimotor loss and areflexia coupled with nerve conduction findings of demyelination essentially defines the illness. Elevated spinal fluid protein concentration is so frequent that it might be added as a diagnostic criterion. The typical findings in nerve conduction studies are of multifocal conduction block as described in Chap. 2; prolonged distal latencies (“distal block”); nerve conduction slowing to less than 80 percent of normal values in several nerves; loss of late responses; and dispersion of the compound muscle action potentials—all reflecting demyelination in motor nerves. One or several of these changes have been present in 75 percent of our patients (Gorson et al, 1997). In the early stages of the disease, demyelinating features must be carefully sought by testing multiple nerves at several sites along their courses. After several months there is often some degree of axonal change (30 percent of our series), but the fundamental process continues to be one of multiple foci of demyelination. A fairly dependable finding is the absence of denervation changes early in the illness despite weakness and reduced amplitude of the motor action potential (indicative of a demyelinating block to conduction at a proximal site).
Several large series of CIDP cases are available for review. Dyck and colleagues (1975) studied 53 patients in whom the neuropathy progressed for more than 6 months. The clinical course was monophasic and slowly progressive in about one-third, stepwise and progressive in another third, and relapsing in the remaining third. The periods of worsening or improvement were measured in weeks or months. Weakness of the limbs, particularly of the proximal leg muscles, or numbness, paresthesias, and dysesthesias of the hands and feet were the initial symptoms. In 45 of the 53 patients, the signs were those of a mixed sensorimotor polyneuropathy with weakness of the shoulder, upper arm, and thigh muscles in addition to motor and sensory loss in the distal parts of the limbs. In 5 patients the neuropathy was purely motor, and in 3, purely sensory. Cranial nerve abnormalities were distinctly unusual. Enlarged, firm nerves were found in 6 patients. Not emphasized in their series is the common occurrence of a cerebellar-like tremor in cases of long standing.
In the series reported by McCombe et al (1987a and 1987b) comprising 92 patients, two major subgroups were recognized: relapsing (corresponding to the relapsing and stepwise progressive cases of Dyck et al [1975]) and nonrelapsing ones. In our own series of now over 100 patients, we have been impressed with several variant patterns of clinical presentation. In approximately 10 percent, numbness and weakness of the hands preceded involvement of the feet, which is unusual in other polyneuropathies, and a sensory ataxic form, a purely motor form, and mononeuropathies superimposed on a mild generalized polyneuropathy each accounted for approximately 5 percent.