Tendinopathy Mimicking Neuropathy on Nerve Conduction Study and Resolved with Ultrasound-guided Steroid Injection: A Case Report

Research Objectives: To describe an incidental finding of low compound muscle action potential (CMAP) amplitude on nerve conduction study (NCS), mimicking neuropathy in a patient suffering from acute tendinopathy

Design: Case Report

Setting: University hospital outpatient clinic

Participants: A 41 year old male suffering from acute lateral ankle tingling pain with weakness in performing ankle eversion and toe extension, one day after walking 8km.

Interventions: Nerve conduction study (NCS) was ordered to determine the source of the symptom and to identify whether peripheral neuropathy was present. On initial finding, there was reduced compound muscle action potential (CMAP) amplitude during peroneal nerve stimulation. Ultrasound of ankle revealed normal peroneal nerve and lateral ligament structures, however tenosynovitis over extensor digitorum longus (EDL) was noted. Intervention with ultrasound-guided injection of triamcinolone and lidocaine into tendon sheath was performed.

Main Outcome Measures: Visual Analogue Scale (VAS), Manual Muscle Testing (MMT), Nerve Conduction Study, Ultrasound Imaging

Results: Pain relief was immediate with decreased VAS after ultrasound-guided injection. Weakness and difficulty of toe extension and ankle eversion was resolved. On one month follow-up, CMAP amplitude was restored and ultrasound imagining showed normal EDL and peroneal nerve without swelling or signs of tenosynovitis. In addition, complete relief on VAS and restoration of muscle strength were noted.

Conclusions: To the best of our knowledge there is limited report on tendinopathy and pain depicting as reduced CMAP amplitude on NCS and mimicking peripheral neuropathy. We demonstrated pain relief after ultrasound-guided steroid injection on tendon sheath and restoration of CMAP amplitude on follow-up NCS. The value of this case is to remind physicians to pay attention to this possible pain factor and avoid misinterpretation of NCS. Further research is needed to clarify the peripheral effect of pain on muscle excitability, contraction, muscle length, and its relationship to CMAP amplitude waveform.

Author(s) Disclosures: No conflicts of interest or financial disclosures.