A new magnetic resonance protocol shows unorthodox patterns of neuropathic pain in Sjögren syndrome, often without underlying evidence of actual neuropathy. This may suggest new treatment targets.
Birnbaum J, Duncan T, Owoyemi K et al.Use of a Novel High-Resolution Magnetic Resonance Neurography Protocol to Detect Abnormal Dorsal Root Ganglia in SjÃ¶gren Patients With Neuropathic Pain: Case Series of 10 Patients and Review of the Literature. Medicine. (2014) 93:121–134 doi: 10.1097/MD.0000000000000024
In a case-series of 10 SjÃ¶gren’s syndrome (SS) patients with proximal neuropathic pain, these authors evaluated patients using a novel magnetic resonance (MRN) protocol which can detect abnormalities of the dorsal root ganglia (DRG). Of these 10 patients, half had radiographic DRG abnormalities.
Interestingly, fornine of these 10 patients who had neuropathic pain, electrodiagnostic and punch skin biopsy studies were normal. The presence of normal skin biopsy studies indicated that there was no degeneration of nociceptive, small-fiber nerves. The finding suggests functional mechanisms that can target the DRG.
“These findings reflect that SjÃ¶gren’s patients can have neuropathic pain without having a neuropathy,” Julius Birnbaum MD, Associate Director of Johns Hopkins Jerome L. Greene SjÃ¶gren’s Syndrome Center told Rheumatology Network. An additional finding was that the subset of 5 patients with abnormal MRN DRG studies had statistically significantly higher nerve-fiber densities compared to the others whose radiographic studies were normal. The authors posited that this may reflect the influence of trophic factors, which are known to cause neuropathic pain. If true, this could be a therapeutic target.
Six patients (two with abnormal DRG) who received intravenous immunoglobulin (IVIg) treatment had a significant reduction in pain (8.2 to 4.0 on the visual analog scale). Two patients treated with IVIg also had corresponding radiographic improvement on serial MRN DRG studies. Four patients who received symptomatic treatment only (due to the refusal of insurance companies to reimburse IVIg treatment) had no improvement.
A detailed literature review showed that whereas up to 40% of SS patients have neuropathic pain, the prevalence of neuropathies was comparatively lower, reported as 1-10% in most studies. These findings support the authors’ assertion that many SjÃ¶gren’s patients have neuropathic pain without underlying markers of a peripheral neuropathy. In such cases, MRN DRG studies may prove important.
Finally, the authors demonstrated how SS patients may have unorthodox neuropathic pain patterns that can affect the face, torso, and proximal extremities. These findings challenge the paradigm that neuropathic pain presents in a distal, “stocking-and-glove” distribution.