LOS ANGELES, California—Fibromyalgia (FM) patients with evidence of chronic inflammatory demyelinating polyneuropathy (CIDP) may benefit from treatment with intravenous immunoglubulin (IVIg), according to a small study in Rheumatology.1

"This FM/CIDP subset may constitute a significant portion of the overall, nonhomogenous family of FMS. Furthermore, it is readily identifiable, and may be responsive to IVIg, a known immune modulator."—Xavier J. Caro, MD.
"This FM/CIDP subset may constitute a significant portion of the overall, nonhomogenous family of FM syndrome. Furthermore, it is readily identifiable, and may be responsive to IVIg, a known immune modulator," conclude researchers led by Xavier J. Caro, MD, associate clinical professor of medicine of the David Geffen School of Medicine at the University of California at Los Angeles.

The new study comprised 58 FM patients, 26 rheumatic non-FM patients, and 52 nonrheumatic, non-FM patients. All patients answered questionnaires regarding paresthesias, subjective weakness, pain, fatigue, and stiffness. A Wartenberg pinwheel and a128 Hz tuning fork identified stocking hypesthesia. The researchers used objective measures of tenderness, proximal muscle strength, and electrodiagnostic (EDX) evidence of polyneuropathy and demyelination to identify FM subjects who had clinical findings suggestive of CIDP. In addition, 11 other FM patients underwent sural nerve biopsy.

Subset of FM patients identified

The study found that paresthesias, subjective weakness, and stocking hypesthesia were more common in FM patients than in rheumatic non-FM patients. Specifically, 76% of FM patients said they had paresthesias compared with just 20% of rheumatic patients without FM. Moreover, 88% of the FM patients had stocking distribution hypesthesia. By contrast, no patients in the rheumatic non-FM group had stocking distribution hypesthesia. Proximal muscle strength was also significantly less in FM patients than in rheumatic non-FMS patients, the study showed.

EDX testing showed a distal demyelinating polyneuropathy, suggestive of CIDP in 33% of the FM patients. There was no polyneuropatyhy or demyelination seen among the rheumatic non-FM patients.

"We found a clear difference in terms of polyneuropathy and demylination when comparing patients with and without fibromyalgia," Dr. Caro told MSKreport.com. A significant number of all-comers with FM had demyelination. “The importance of these findings” added Dr. Caro, “rests with their strengthening of a growing body of medical literature showing that immune dysregulation makes up an important component of FM syndrome. This finding also has significant implications for the treatment of FM.”

FM/CIDP patients may be candidates for IVIg. "Since IVIg is the treatment of choice for CIDP, it stands to reason that these patients may be candidates for IVIg treatment if they can tolerate it.”

IVIg improved tenderness, strength

A total of 15 FM/CIDP subjects were subsequently treated with IVIg at 400 mg/kg QD for 5 days as part of the study. Pain (P = .01), tenderness (P = .001), and strength (P = .04) improved significantly; fatigue and stiffness trended toward improvement.

"We have treated a number of CDIP patients with IVIg now, including the 15 in the paper, and we have had good to excellent responses," he said.

Reference
1. Caro XJ, Winter EF, Dumas AJ. A subset of fibromyalgia patients have findings suggestive of chronic inflammatory demyelinating polyneuropathy and appear to respond to IVIg. Rheumatology. 2008;47:208-211.