Persistent idiopathic facial pain exists independent of somatosensory input from the painful region: findings from quantitative sensory functions and somatotopy of the primary somatosensory cortex.

In 14 patients with unilateral persistent idiopathic facial pain (PIFP), classified according to the criteria of the International Headache Society, and 16 age-matched control subjects sensory functions were examined on the face by quantitative sensory testing (QST). Additionally, the somatotopy of the primary somatosensory cortex (SI) to tactile input from the pain area was evaluated by means of magnetoencephalography. Previously reported abnormalities in PIFP as a dishabituation of the R2 component of the blink reflex and psychiatric disturbances were co-evaluated. Psychiatric evaluation included a Structured Clinical Interview for axis-I DSM IV disorders (SCID-I) and employment of the SCL-90-R and a depression scale (ADS). Thresholds to touch, pin prick, warm, cold, heat and pressure pain as well as the pain ratings to single and repetitive (perceptual wind up) painful pin prick stimuli did not indicate a significant sensory deficit or hyperactivity in the pain area when compared with the asymptomatic side nor when compared with the values of healthy control subjects. QST results were not significantly altered in patients (n=4) that showed an abnormal dishabituation of the R2 component of the blink reflex. The interhemispheric difference in distance between the cortical representation of the lip and the index finger did not differ between patients and control subjects. Psychiatric evaluation did not disclose significant abnormalities at a group level. It is concluded that PIFP is maintained by mechanisms which do not involve somatosensory processing of stimuli from the pain area.