By Eleanor McDermid, Senior medwireNews Reporter
Half of patients referred to a specialist centre with a diagnosis of chronic inflammatory demyelinating polyneuropathy (CIDP) do not actually have the condition, report researchers.
Of 58 patients referred, just 31 (53%) at least possibly satisfied the European Federation of Neurological Societies/Peripheral Nerve Society (EFNS/PNS) criteria for CIDP, while 27 (47%) did not even meet the minimum criteria. Patients with a correct diagnosis were most frequently referred by a neuromuscular specialist.
Although 44% of the misdiagnosed patients satisfied the clinical EFNS/PNS criteria, all were atypical presentations. Just 14.8% of the misdiagnosed patients met the electrodiagnostic criteria, compared with all of the confirmed CIDP patients.
“It is critical that the CIDP diagnosis with atypical clinical features be based on both clinical and electrophysiologic abnormalities”, say study authors Jeffrey Allen (University of Minnesota, Minneapolis, USA) and Richard Lewis (Cedars-Sinai Medical Center, Los Angeles, California, USA).
The researchers highlight several common diagnostic errors, including “misinterpretation of electrodiagnostic studies”. Rather than clear demyelination, misdiagnosed patients most often had length-dependent axonal polyneuropathy, focal or multifocal demyelination that was limited to compressible sites, and abnormalities only affecting motor nerves. All these findings were better explained by conditions other than CIDP, says the team in Neurology.
Another problem was “placing an overstated importance on mild or moderate cytoalbuminologic dissociation”. Although cerebrospinal fluid protein levels were often increased in both groups, the elevations were generally mild or moderate in misdiagnosed patients, at an average of 61.4 mg/dL versus 156.3 mg/dL in correctly diagnosed patients, with only two exceeding levels of 100 mg/dL.
A third error was “hypervigilance of subjective patient-reported perception of treatment benefit”, say the authors.
Twenty-one misdiagnosed patients were treated with intravenous immunoglobulin or corticosteroids, for an average of 1.5 years. During treatment, 85.7% of misdiagnosed and 89.6% of correctly diagnosed patients reported at least a probable subjective improvement, although fewer misdiagnosed patients reported a definite improvement, at 66.7% versus 89.6%.
But a significant difference only emerged for objective measures of strength/sensation improvement, which occurred in just 19.0% of misdiagnosed patients, compared with 68.9% of those with confirmed CIDP. And the four misdiagnosed patients with objective treatment responses were reclassified for other reasons, to multifocal motor neuropathy, multiple sclerosis, neurosarcoidosis, and stiff-person syndrome.
Editorialists Kenneth Gorson (Tufts University School of Medicine, Boston, Massachusetts, USA) and Clifton Gooch (University of South Florida, Tampa, USA) say: “The fact that so many patients labeled with CIDP had non-neuropathic conditions is worrisome, raising fundamental questions regarding the adequacy of neuromuscular education and practice of contemporary neurologists that will not be remedied easily.
“This study implies that the educational curriculum of neurology residency programs should be strengthened in neuromuscular disease and electrodiagnosis.”
But they say the findings suggest some tactics to improve diagnosis, including adherence to guidelines, extensive and stringent testing of nerves, adherence to proper treatment regimens with objective measures of treatment response, and review in the case of sustained response or nonresponse.
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