Three years after a cubital procaine-HCL 0.05% injection had caused acute severe local pain radiating to his forearm and wrist, a 33-year old man complained about pain in his right hand. Two months later, he also suffered from numbness in the distribution of the right median nerve and wasting of thenar muscles. Furthermore a muscular atrophy in his right forearm was noted. Nerve conduction studies showed an increased distal latency in the median nerve, a very low thenar compound muscle action potential on median nerve stimulation, a reduced sensory conduction velocity of 39 m/s in the median nerve on thumb stimulation and no sensory nerve action potential on stimulation of the 2nd and 3rd fingers. Electromyography of the right biceps brachii muscle was normal. In the fibrillations, an increased duration and amplitude of motor unit potentials and reduced recruitment pattern were found in the right abductor pollicis brevis muscle. Forearm muscles were not investigated. A carpal tunnel syndrome was diagnosed and treated by surgery.
Ten months later the patient was admitted to our department because of persistence of his symptoms. Nerve conduction studies showed no response over the thenar muscle on median nerve stimulation at the wrist and elbow. Fibrillations and sparse motor unit potentials with increased duration and amplitude (up to 10 mV) were found in flexor digitorum superficialis muscle, in contrast to the normal Electromyography-findings of the right flexor carpi ulnaris. On median nerve stimulation at the elbow a low compound muscle action potential with an increased distal latency was recorded over flexor digitorum superficialis muscle in the right side (right: amplitude 1 mV, latency 9.0 ms, left: amplitude 7 mV, latency 3.2 ms). No sensory nerve action potential was recorded at the wrist on stimulation of the 1st, 2nd or 3rd finger. Somatosensory evoked potentials of the left median and right radial and ulnar nerve were normal. No potential was recorded at Erb's point in the supraclavicular fossa, at the sixth and second cervical vertebra and the contralateral cortex on median nerve stimulation on the right.
Proximal median nerve lesion was suggested. Palpation along the median nerve revealed a fusiform mass at the distal third of the right upper arm, which could be confirmed by MRI (see figure 1 and 2).
Surgical resection of a 7 cm long segment of the median nerve with the tumorous lesion and replacement with a sural nerve graft was undertaken. Resection was necessary because of severe involvement of fascicles without any possibility to separate the tumour from the median nerve by micro-surgery. Histological investigation revealed marked peri- and endoneurial fibrosis, severe axonal loss as well as proliferation of concentric whorl-like formations resulting in multicompartment arrangement. These pseudo onion-bulb formations showed strong immunoreactivity for the epithelial membrane antigen and were predominantly negative for S-100 protein, suggesting a proliferation of perineurial cells rather than Schwann cells. In addition, small groups of regenerating axonal sprouts surrounded by perineurial ensheathment were visible, indicating some neuroma-like component (see figure 3 and 4).
The tumour was diagnosed as perineurioma and additional neuroma by histopathology. On clinical follow-up four years later a partial recovery of forearm muscle strength could be noted and the patient was free from pain.