Introduction
Myofascial trigger point injections are frequently indicated for myofascial pain syndrome and are performed as blind procedures. Although these injections are usually safe and effective, complications resulting in pneumothorax, epidural abscess, skeletal muscle toxicity, intrathecal injection, and nerve injury has been reported. We report a patient with radial nerve injury after blind myofascial trigger point injection.
Case report
A 53-year old man referred to the Department of Rehabilitation Medicine to evaluate his left wrist drop. He has no significant past medical history. He visited a local clinic to manage his left shoulder pain. He was given an injection on his shoulder. But the pain continued, and he underwent a blind myofascial trigger point injection on his left shoulder, elbow, forearm, and hand. Since then, the left wrist drop has appeared.
On manual muscle strength testing, abduction of left 5th finger, radial deviation of the 2nd finger and finger extension were severely weak but extension and flexion of wrist, supination, and pronation of forearm and extension of the elbow were normal. There were no hypesthesia, tingling sensation. On physical examination, there were no tinel's sign at wrist, elbow and radial nerve.
For further evaluation, we performed electromyography to evaluate the injury of the left radial nerve. During needle electromyography, abnormal spontaneous activities were observed in the extensor indicis proprius and extensor digitorum communis. Triceps brachii, extensor carpi radialis longus, and brachioradialis muscle were normal. On the motor nerve conduction study, the left radial nerve showed low compound muscle action (CMAP) and slow conduction velocity. On the sensory nerve conduction study, the superficial radial sensory nerve action potential (SNAP) was normal. After the electromyography, the symptom improved mildly and he has undergone medication and joint exercises to prevent the complication.
Conclusion
Clinically posterior interosseous neuropathy (PIN) usually occurs as an entrapment under the tendinous Arcade of Froshe. Rarely other mass lesions result in PIN. In this case, we suspect a nerve injury by injection. Therefore, although blind myofascial trigger point injection is known to be relatively safe, we advise performing ultrasound-guided injection to prevent complications.
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