In sural nerve biopsy material, half are found to have interstitial and perivascular infiltrates of inflammatory cells, although one expects that most nerves would show these changes if a sufficient number could be sampled. Some specimens show only demyelination, or in cases of long standing, severe depletion of all nerve fibers. As in GBS, the demyelination appears to be affected by T cells and macrophages within the endoneurium and perineurium. The loss of myelinated fibers is variable and many of the remaining fibers are seen to be undergoing wallerian degeneration or show changes of segmental demyelination or demyelination-remyelination. Onion-bulb formations are conspicuous in recurrent and relapsing cases. The few adequate autopsy studies have shown only minimal or patchy inflammation and a considerable degree of axonal damage, probably reflecting the long duration of illness before examination. The presence of endoneurial and subperineurial edema has been emphasized by
Prineas and McLeod.
Treatment Several trials have shown a short-term benefit from the intravenous infusion of high doses of gamma globulin (IVIg, total 2 g/kg in divided infusions over 2 to 5 days), see Hahn et al 1996b. More than half of our patients have responded to this treatment, albeit for only several weeks or months, after which the infusions must be repeated to maintain clinical improvement. A desire to spare patients the side effects of indefinite prednisone administration (see later) makes this mode of therapy a reasonable alternative, in some cases for almost 10 years without ill effects. Patients who require treatment at such short intervals as to be impractical have benefited from the addition of small doses of prednisone or of an immunosuppressive drug as described in the following text. The main drawbacks of IVIg are its expense and the several hours required for its infusion. Rare instances of nephrotic syndrome, aseptic meningitis, serum sickness, thrombotic venous, or arterial occlusion, including stroke and hypotension, have been reported, particularly if the infusion is too rapid.
Half of patients with CIDP also respond well to plasma exchanges. In a prospective double-blinded trial, Dyck and colleagues (1986a) found that plasma exchange administered twice weekly for 3 weeks had a beneficial effect on both neurologic disability and nerve conduction. The response to plasma exchange in our patients has been comparable to that obtained with IVIg and with steroids, but we have discerned that some patients respond to one type of treatment and not another. The effects of plasma exchanges in most patients subside in 10 to 21 days, or even less; in some, the response lasts longer as found by Dyck and colleagues (1986a) and in the series reported by Hahn and colleagues (1996a). For these reasons we have often tried plasma exchange or immune globulin before committing a patient to long-term treatment with prednisone. The relative ease of administering IVIg favors its use first, followed by a series of plasma exchanges if there is no improvement. When there is a clear response, 3 or 4 brief series of plasma exchanges or repeated infusions of immune globulin may suffice to bring the patient to an improved level of function. These treatments can be supplemented by small doses of prednisone when frequent infusions or exchanges become impractical. It has been our experience that in about one-third of cases, IVIg and plasma exchange cease to have benefit after repeated use for 1 or more years. The ideal regimen for either treatment has not been established and is often guided by the clinical examination and reports from the patient about return of symptoms after an interval of weeks or months after each treatment. One of the most difficult problems in this field is the lack of useful clinical measurements to guide treatment with IVIg and plasma exchange and even the proper adjustment of the dose of corticosteroid. Often, one may be influenced by the patient’s fear of losing any ground and even slight changes in sensory or motor symptoms.