IC/PBS patients are more sensitive to pain, according to a new study

Key Points

San Francisco-Italian researchers say they have some direct evidence for central sensitization in interstitial cystitis/painful bladder syndrome (IC/PBS). Central sensitization-essentially amplification of pain signals in the central nervous system-is thought to contribute to perpetuation of pain-and possibly its initiation-in the condition.

That theory may help explain the connection between IC/PBS and often-concomitant visceral and somatic conditions such as irritable bowel syndrome and fibromyalgia. The theory also has prompted research to focus on drugs affecting the CNS for refractory IC/PBS and other chronic pain conditions.

As reported at the International Continence Society annual meeting, Silvia Malaguti, MD, and Mauro Cervigni, MD from San Carlo-IDI Hospital, Rome, investigated spinal transmission of pain signals and diffuse noxious inhibitory controls in 14 IC/PBS patients-12 women and two men-and in 10 age- and sex-matched healthy controls.

The investigators did this using the nociceptive flexion reflex (NFR) RIII and the cold pressor test (CPT), both of which are standard tests in pain research.

The NFR is administered by electrically stimulating the sural nerve. The test's RIII, or long-latency, component is evoked by stimulation intense enough to activate the A-delta and C fibers responsible for transmission of pain signals. Thresholds for the reflex correlate strongly with subjective pain thresholds, and increases in NFR amplitude correlate with increases in subjective pain intensity.

In the CPT, the patient places a hand in ice water. The patient lets the researcher know when he/she first feel pain and then withdraws the hand when the pain becomes unbearable. This measures a threshold for and tolerance of this type of pain. In this study, the CPT was used as the noxious conditioning stimulus. The investigators measured the NFR RIII at baseline and then during the CPT.

Significantly lower pain thresholds

The IC/PBS patients had significantly lower subjective pain thresholds and significantly lower NFR RIII reflex thresholds than the controls. Moreover, in controls, the NFR RIII reflex was significantly inhibited (down 39%) during the CPT, but in the IC/PBS patients, the NFR RIII reflex did not decrease and was actually stronger (up 35%) during the CPT.

Apparently, patients with IC/PBS do modulate pain differently from those without the condition.

"Of course, we are interested in expanding the study to more patients," said Dr. Cervigni, chief of urogynecology at San Carlo-IDI Hospital. "And we're following up our initial group of patients to see how this mechanism is involved in the natural history of IC."