About forty percent of the patients with primary Sjögren's syndrome (pSS) experience chronic neuropathic pain with normal electrodiagnostic studies. Two previous studies suggest that chronic neuropathic pain in pSS is due to small fiber neuropathy (SFN). Quantification of epidermal nerve fiber density after skin biopsy has been validated to diagnose small fiber neuropathy.
Skin biopsy was performed in 14 consecutive pSS patients (satisfying the american-european classification criteria) with chronic neuropathic pain and normal electrodiagnostic studies suggesting SFN.
Fourteen female pSS patients exhibited chronic neuropathic pain [burning sensation (n=14), prickling (n=4), dysesthesia (n=8)] with paroxystic exacerbations (n=10) and allodynia (n=13), for a mean period of 18.4±12.4 months. Neuropathic pain involved mostly hands and feet (n=13), with a distal (n=9) and leg (n=4) predominant distribution. Neurological examination disclosed normal deep tendon responses and absence of motor weakness (n=14). Small fiber neuropathy was confirmed by skin biopsy in 13 cases. Epidermal nerve fiber density was decreased in distal [(n=12), mean 3.5±1.7 fibers/mm (N>6.9)] and proximal site of biopsy [(n=9), mean 7.04±2.63 fibers/mm (N>9.3)].
Small fiber neuropathy is commonly responsible of chronic neuropathic pain in pSS. Prevalence, physiopathology and neurological evolution of such neuropathies still remain unknown.