Somatosensory hypersensitivity in the referred pain area in patients with chronic biliary pain and a sphincter of Oddi dysfunction: new aspects of an almost forgotten pathogenetic mechanism.

BACKGROUND AND AIMS: Somatosensory hyperalgesia in the referred pain area (RPA) in patients with acute or chronic abdominal pain syndromes may result from the convergence of nerve fibers from visceral and somatic tissues at the spinal and supraspinal levels. Chronic biliary pain in patients with the postcholecystectomy syndrome (i.e., biliary hypersensitivity) may be explained by persistent hyperexcitability of neurons in the central nervous system (CNS). The aim of this study was to evaluate the cutaneous neural sensory perception in the RPA in patients with chronic postcholecystectomy biliary pain and a sphincter of Oddi (SO) dysfunction (SOD).
METHODS: Forty-two patients with persistent biliary pain and suspected SOD, 27 age-matched healthy volunteers, and 18 age-matched asymptomatic cholecystectomized controls were prospectively investigated by quantitative sensory testing (Neurometer CPT). The biliary symptoms and the severity of pain were classified on a visual analog pain severity scale system via a previously validated and standardized questionnaire. The patients helped the doctors locate the RPA in the right upper quadrant. The sensory detection threshold was determined noninvasively (Neurometer CPT) with transcutaneous electrical stimulation at 5, 250, and 2,000 Hz, and different current intensities (range from 0.01 to 9.99 mA) applied in a single (patient) blinded method. These three frequencies selectively excite small unmyelinated (C fibers), small myelinated (A-delta), and large myelinated (A-beta) fibers, which transmit dull pain, sharp pain, and touch, respectively. The contralateral region of the abdomen left upper quadrant served as the control area. The sensory current perception threshold ratio (SCPTR) of the data measured in the contralateral area and the RPA was calculated.
RESULTS: The SCPTRs in the definite SOD patients with biliary pain, healthy volunteers, the asymptomatic cholecystectomized controls, and the symptomatic cholecystectomized patients but without SOD were 2.32 +/- 1.4 versus 1.06 +/- 0.24 versus 0.97 +/- 0.16 versus 0.83 +/- 0.35 at 2,000 Hz; 2.19 +/- 1.0 versus 1.01 +/- 0.26 versus 1.02 +/- 0.25 versus 0.88 +/- 0.35 at 250 Hz; and 2.19 +/- 1.1 versus 1.12 +/- 0.26 versus 0.99 +/- 0.37 versus 0.84 +/- 0.32 at 5 Hz, respectively. Significant hypersensitivity was detected in the RPA at different stimulation frequencies in the SOD patients with biliary pain versus the cholecystectomized controls: at 5 Hz: P = 0.00001; at 250 Hz: P = 0.00001; and at 2,000 Hz: P = 0.0001, respectively.
CONCLUSION: Continuous visceral pain (biliary pain) caused by local inflammatory/sensitizing processes or a CNS malfunction could lead to significant hypersensitivity of the peripheral nociceptive nerve fibers in SOD patients. Postcholecystectomy pain may be explained by persistent hyperexcitability of the nociceptive neurons in the CNS with or without objective motility disorders of the SO.