Small-fiber neuropathy is one of the most common types of peripheral neuropathy affecting patients with systemic lupus erythematosus, but it isn’t even mentioned in the American College of Rheumatology neuropsychiatric case definitions of manifestations of the disorder, according to a retrospective analysis of cohort of 2,097 patients with SLE.
Other types of peripheral neuropathy, such as acute inflammatory demyelinating neuropathies (for example, Guillain-Barré syndrome), plexopathies, and mononeuritis multiplex, are well described in the ACR-NPSLE case definitions but occur much less frequently. This, combined with the fact that small-fiber neuropathies often present as "unorthodox" pain patterns, indicates that they are underdiagnosed, said Dr. Amin Oomatia of the University of Cambridge, England, and his coinvestigators at John Hopkins University, Baltimore.
Small-fiber neuropathies arise through mechanisms that are distinct from those of other neuropathies and require different diagnostic strategies to be properly identified. In particular, small-fiber neuropathies do not always conform to the "stocking-and-glove" pattern of pain that is typical of other neuropathies in SLE, so it is likely that many affected patients "may be regarded in routine clinical care as having a ‘nonorganic’ pain disorder.
"Our findings suggest that rheumatologists and other clinicians who confront SLE patients with seemingly improbable pain patterns should consider the diagnosis of a small-fiber neuropathy," the investigators wrote, especially since it may occur in the face of normal electrodiagnostic studies.
Dr. Oomatia and his colleagues based these conclusions on their retrospective study of one medical center’s 25-year experience treating 2,097 SLE patients – the Johns Hopkins Lupus Cohort. Using details in a database of patients’ electronic medical records, they identified 82 patients who had peripheral neuropathies related to SLE.
Only one patient had peripheral neuropathy attributable to Guillain-Barré syndrome, only one patient had a plexopathy, and only six patients had mononeuritis multiplex, demonstrating that these are very infrequent complications of SLE even though they are included in ACR case definitions.
In contrast, 14 patients (17% of those with peripheral neuropathy) had biopsy-proven small-fiber neuropathies, and most of them presented with "an entirely different and unorthodox pain distribution" characterized as patchy, asymmetric, or proximal.
In particular, nine patients had pain affecting the face, torso, and/or proximal extremities. Three had burning pain over their entire bodies, the investigators said (Arthritis Rheum. 2013 Dec. 10 [doi:10.1002/art.38302]).
In these cases, punch skin biopsy showed abnormalities that disproportionately affected the proximal thigh, "which is considered a surrogate indicator of proximal-most dorsal root ganglia neuronal cell loss," they wrote. In contrast, other patients who had the typical distal pattern of neuropathic pain showed decreased intraepidermal nerve-fiber densities in the distal leg, a surrogate indicator of distal-most axonal degeneration.
Another distinguishing feature of small-fiber neuropathy was its association with a history of herpes zoster virus, opportunistic infections, and osteoporotic fractures, all unrelated to corticosteroid dose, Dr. Oomatia and his associates said.
This study was supported in part by the National Institutes of Health and the National Center for Research Resources. No potential financial conflicts of interest were reported.