- Small fiber polyneuropathy (SFPN) is increasingly recognized as a contributor to other pain syndromes
- In a Mass General study, 25 of 39 patients (64%) with complex chronic pelvic pain (CPP) had SFPN detected on skin biopsy
- Those 25 patients had refractory lower urinary tract symptoms and abnormal results on video urodynamic testing
- Further research is needed to determine whether SFPN is a mechanism for pain in patients with complex CPP
Small fiber polyneuropathy (SFPN), an emerging clinical entity, is increasingly recognized as a major contributor to multisymptom chronic pain syndromes. For example, SFPN is found in one-third to one-half of patients with fibromyalgia.
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Common symptoms of SFPN, which are often worse at night, include vague distal sensory disturbances, burning pain in the extremities and autonomic and enteric dysfunction. Using a skin biopsy specimen, a specialized laboratory can apply multimolecular immunofluorescence to diagnose SFPN.
For the first time, researchers at Massachusetts General Hospital have demonstrated a link between SFPN and complex chronic pelvic pain (CPP), which itself is often associated with other pain syndromes. Clinicians who are alert to this potential co-diagnosis may be able to spare CPP patients some of the frustration that arises from lack of improvement—or even worsening—with standard treatments.
Urologist Elise De, MD, and colleagues retrospectively reviewed a prospective database of 39 consecutive patients with CPP who were offered a diagnostic skin biopsy in subspecialty clinics at Albany Medical Center. All patients had experienced at least six months of pelvic pain despite initial treatment or presented with multiple concurrent pain syndromes. Neuropathy was ruled out.
Twenty-five of the 39 patients (64%), including two of three men, tested positive for SFPN, the researchers report in Pain Medicine. These patients described their pain as one or more of the following:
- Pain with full bladder
- Urethral pain during and after voiding
- Pain on the vulvar or scrotal surface
- Pain deep inside the vagina, penis or rectum either during sexual activity or at rest
- Pain with bowel movement
- Persistent pain below the umbilicus (not because of another cause)
A number of other painful conditions were highly prevalent in SFPN+ patients:
- Gastroesophageal reflux disease (46%)
- Fibromyalgia (38%)
- Migraine (38%)
- Irritable bowel syndrome (33%)
- Lower back pain (33%)
- Interstitial cystitis (18%)
- Endometriosis (15%)
- Vulvodynia (5%)
Fifteen of the 25 SFPN+ patients underwent video urodynamic testing for refractory lower urinary tract symptoms. The results were abnormal in all of them: nine exhibited obstructions referable to the bladder, and six were unable to mount a detrusor contraction, which can also be a sign of bladder neck obstruction.
Many of these patients did not benefit from these standard interventions:
- Alpha blockers—six of ten improved
- Downtraining with physical therapy—four of ten improved
- Onabotulinum toxin A to the levator muscles—one of six improved
- Onabotulinum toxin A to the bladder neck—one of two improved
- InterStim therapy—one of two improved
This retrospective study does not support a causative relationship between SFPN and CPP, the researchers note. Still, they recommend that when a patient with complex CPP has multiple pain syndromes or does not respond to standard first-line treatment, a simple skin biopsy should be evaluated for SFPN. Future research may lead to tailored treatment options.
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