Introduction
Median neuropathy above wrist level is uncommon when compared with the median entrapment neuropathy at the wrist. Differentiating between median neuropathy at the wrist and above wrist level may be difficult when relying only on physical examination, so electrodiagnostic study is important tool in localizing the lesion in proximal median neuropathy. Here, we present a case report of lipomatosis of median nerve mimicking carpal tunnel syndrome, in which electrodiagnostic study played an important role in diagnosis.
Case report
A 38-year-old woman visited our institution presenting symptoms of hypoesthesia and paresthesia at right thumb and index finger, which started 6 months ago. During 6 months, she had visited local clinics and received injection therapy under impression of cervical radiculopathy and carpal tunnel syndrome. Because the symptoms persisted despite of the therapy, she visited our institution and was referred to rehabilitation department for electrodiagnostic evaluation. On physical examination, there was no motor weakness at both upper extremities, but light touch sensation of right thumb and 2nd finger was decreased. Tinel sign at wrist was positive at right side, but other physical examination showed no significant findings. Cervical spine x-ray showed degenerative change with cervical straightening.
On the nerve conduction study(NCS), the right median sensory NCS in the digit III was normal, but the right median sensory NCS in the digit II and thumb showed decreased amplitudes when compared with the left side. The right median motor NCS to abductor pollicis brevis muscle showed conduction block and decreased conduction velocity between wrist and elbow segment. The right median motor NCS to pronator quadratus muscle showed no abnormal findings (Table 1). On needle electromyography, abnormal spontaneous activities were noted in the right abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis muscles (Table 2). The patient was diagnosed with right median neuropathy above the wrist level.
Magnetic resonance imaging (MRI) of right wrist was done, and collection of slightly enlarged nerve fascicles along the course of median nerve was surrounded by high signal fat, which showed spaghetti-like appearance (Figure 1). With the diagnosis of lipomatosis of median nerve, she underwent the surgery of median nerve neurolysis wih lipoma excision.
Conclusion
Lipomatosis of peripheral nerve is rare disorder involving diffuse infiltration of peripheral nerves with fibrous and adipose tissues. When involving median nerve, clinical symptoms may be similar to those of carpal tunnel syndrome, and may lead to different treatment. Electrodiagnostic study is one of the useful diagnostic tools in localizing the lesion, and can lead to proper management.
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Table 1. Sensory and Motor Nerve Conduction Study
Table 2. Needle Electromyography Study
Figure 1. Magnetic resonance imaging (MRI) of right wrist. (A) Coronal T2-weighted image of right wrist. (B) Axial T2-weighted image of right wrist. Collection of slightly enlarged nerve fasicles along the course of median nerve is surrounded by high signal fat, showing spaghetti-like appearance.
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