Corneal confocal microscopy (CCM) is a novel technique allows for the quantification of small fibers located near the center of the cornea. CCM is noninvasive and fast, and might be a useful method to confirm small nerve fiber pathology. Our objective was to assess corneal small nerve fiber morphology in patients with chronic pelvic pain (CPP) and to determine the prevalence of Small fiber neuropathy (SFN) in patients with chronic pelvic pain using CCM. The interplay between peripheral and central amplifiers is complex. Despite the established association of CPP with these other complex pain syndromes, and even though both periperhal sensitization and central sensitization have been proposed as underlying processes associated with CPP, a definitive explanation for this association according to known pain mechanisms is not well established. The lack of a common underlying mechanism or condition limits a provider’s ability to either reassure the patient or offer effective treatment options. Further elucidation of the pathophysiological mechanisms in patients with refractory and multisystem pain is key to understanding these entities, and will be instrumental in developing efficacious treatment modalities for the millions of people suffering from these conditions [1].

Design. Retrospective study of prospective database.
We studied 22 patients with CPP (male= 14, female = 8) and 10 healthy control subjects. All the participants completed different questionnaires in regards to the symptoms of  chronic pelvic pain including a neuropathic pain survey. A central corneal thickness scan was obtained with a confocal microscope HRT3-RCM, Heidelberg Engineering (Heidelberg, Germany). This confocal microscope uses a diode helium-neon laser with a wavelength of 670 nm as a radiation source. Nerve measurements were made by a single ophthalmologist without knowledge of the clinical diagnosis.

Patients with chronic pelvic pain had stromal nerve thickness of 4.8 ± 1.0 micrometers (mean ± standard deviation) significantly different from control’s values (6.0± 1.3) p = 0.01. Patients also had significant increase in dendritic cell density 10± 2 vs 3± 1 of controls p = 0.01. 
Sixteen of 22 patients with pelvic pain (73%) were positive for SFN using CCM. Comorbid conditions noted in chronic pelvic pain  group included chronic prostatitis (37%), irritable bowel syndrome (32%), migraine (28%), lower back pain (23%), interstitial cystitis (19%), fibromyalgia (14%), vulvodynia (14%), endometriosis (10%).

Patients with chronic pelvic pain have thinner corneal stromal nerves and increase in dendritic cell density when compared to healthy controls. Small fiber neuropathy may play a role in the pathogenesis of chronic pelvic pain.

Corneal confocal microscopy could become a useful test in the study and management of patients with chronic pelvic pain.

Annie Chen, Elise De, Charles Argoff. Small Fiber Polyneuropathy Is Prevalent in Patients Experiencing Complex Chronic Pelvic Pain. Pain Med . 2019 Mar 1;20(3):521-527.