OBJECTIVE: We compared the anti-allodynic effect of Neurotropin^® (an extract from the inflamed skin of rabbits inoculated with vaccinia virus, NTP) with those of anti-inflammatory drugs and anti-depressants in rats with L5 spinal nerve ligation (L5-SNL). Additionally, we investigated the combinational effect of NTP and milnacipran in L5-SNL rats.
METHODS: The left fifth lumbar nerve of rats was tightly ligated with silk sutures under pentobarbital anesthesia. Mechanical allodynia was confirmed by measuring the hindpaw withdrawal threshold in response to the application of von Frey filaments. Behavioral tests were performed at 28 days after nerve ligation. NTP, non-steroidal anti-inflammatory drug (NSAID, loxoprofen), COX-2 inhibitor (celecoxib), selective serotonin reuptake inhibitor (SSRI, paroxetine) and serotonin-noradrenaline reuptake inhibitor (SNRI, milnacipran) were administered orally. Dose-response curves were established and the 30% effective dose values were determined for NTP and milnacipran. An isobolographic analysis was performed to clarify the interaction of NTP and milnacipran.
RESULTS: NTP (400 NU/kg) showed an anti-allodynic action in L5-SNL rats. Loxoprofen (100 mg/kg) and celecoxib (100 mg/kg) had no effect in L5-SNL rats. On the other hand, milnacipran(100 mg/kg) elicited an anti-allodynic action, but paroxetine (10 mg/kg) did not inhibit allodynia in L5-SNL rats. The combination of NTP and milnacipran showed an additive effect in L5-SNL rats.
CONCLUSION: These results suggest that NTP is more effective than NSAID and SSRI, and the combination of NTP with SNRI is useful for treatment of neuropathic pain.

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The author reports a patient with intraoral neuropathic pain after zygomatic bone fracture. A 24-year-old woman had broken the left zygoma due to traffic accident. The fracture had been surgically repaired with a metal plate 4 months before she was referred to the author. She did not have any intraoral pain shortly after the surgery. However, intraoral pain developed 2 months after the surgery and she was referred to the author. An intraoral neurosensory stent was made to cover the painful area. The inner surface of the stent was covered with a gel mixed with topical anesthetics and denture stabilizer. The gel was applied 4-5 times daily to relieve pain. The pain gradually decreased ≤6 weeks after application of the stent. The patient was referred to a psychosomatic physician; thereafter, she received an antidepressant, which dentists are not allowed to prescribe in Japan. The pain was relieved ≤6 months after the medication. Cooperation of physicians and dentists is beneficial to relieve intraoral neuropathic pain.

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We report a patient with cervical spondylotic myelopathy whose pain was confused with whip-lash injury. Pain in the neck, shoulder, arm, lateral chest, and lower extremity on the left side developed in a 66-year-old man 1 month after a traffic accident that occurred 15 years before his referral to our department. The pain gradually worsened. He saw doctors, who thought that the pain was caused by whiplash injury after the traffic accident. The precise initial history taking and physical examination revealed that pain and hypoesthesia were in the neck, shoulder, arm, and lateral chest on the left side, without impairment of muscular strength of the upper and lower limbs. However, the patellar reflex was exaggerated on both sides. MRI of the neck showed narrowed cervical canal at C3/4-6/7. The pain decreased after oral administration of Japanese herbal medicine and repeated brachial plexus blocks. Onset of pain 1 month after the traffic accident and the subtle symptoms of cervical spondylotic myelopathy in this patient seemed to make the diagnosis difficult.

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