Pain in the hand caused by a previously undescribed mechanism with possible relevance for understanding regional pain

Background and aims A previously undescribed mechanism of pain in the ulnar side of the hand was observed in a series of four patients. All were found to have a sensitive point in the first interspace of the hand and possible entrapment of a terminal branch of ulnar nerve piercing the fascia in the first interphalangeal webspace was suggested. Methods Pressure on the sensitive point reproduced the ulnar sided hand pain. Diagnostic and therapeutic injection of the mixture of local anesthetic and corticosteroid were performed. The degree and duration of relief of pain was noted. Results In individuals with recent onset hand pain of this type the injections abolished pain for 2 or more years. In individuals with long-standing pain (longer than 3-6 months) the pain was abolished for periods of time lasting several hours to several weeks. The correspondence of the point, where injections were done with acupuncture point LI4 was noted. Conclusions The location of possible nerve entrapment corresponds with an acupuncture point LI4 and may additionally represent a previously undescribed myofascial trigger point. Implications The suggested mechanism of ulnar sided hand pain represents a miniature chronic constriction injury similar to the animal model of neuropathic pain and may have relevance for regional pain elsewhere in the body.