Successful treatment of pronator syndrome by botulinum toxine injection

The pronator syndrome is a rare proximal entrapment syndrome of the median nerve, characterized by diffuse pain on the volar surface of the forearm, typically exaggerated by pronation of the forearm against resistance. Most frequent etiologies include anatomical abnormalities, occasionally manifested by repetitive pronation of the forearm or bearing of heavy loads. The diagnosis is mainly based on the patients history and clinical findings. Treatment includes immobilization of the forearm, local injections of steroids, non-steroid antirheumatic drugs, and in refractory cases decompression of the nerve. We report about a patient, who was successfully treated by local botulinum injection in the biceps muscle.

The 67-years old male patient reported intermittent pain and a electric feeling on the right-sided forearm, radiating onto the upper arm, and dysaesthesia on his hand. Pain were exacerbated by hand work and especially by breast stroke swimming. Clinical examination revealed no sensomotor deficits. Local pressure to the proximal volar surface of the forearm on the pronator teres muscle was painful, pain also could be provoked by supination of the forearm against resistance. Extension of the elbow against resistance with the forearm in a prone position was painless. Electromyography of the biceps brachii, pronator teres, flexor digitorum superficialis, and abductor pollicis brevis muscles revealed normal findings. We diagnosed a pronator syndrome, probably due to lacertus fibrosus extension from the biceps tendon. We hypothetized that decreasing pull on this band by partial weakness of the biceps muscle might reduced compression on the median nerve and 50 units of botulinum toxine (Botox®, Pharm-Allergan) were injected into the distal lateral part of the biceps brachii muscle. Four weeks after injection the patient registered marked pain reduction, after three month he was totally cured.

Our experience indicates that local botulinum injection might be a therapeutic option in pronator teres syndrome caused by compression by the lacertus fibrosus. Decompression of the nerve is much more likely the mechanism of our therapeutical success than direct influence of the toxine on the nerve. To our best knowledge, treatment of the pronator teres syndrome by means of botulinum toxine injection still has not been reported in literature.