PMC8457354_01
Muscle atrophy of bilateral supraspinatus and infraspinatus. The bilateral infraspinatus fossae are dented, with greater severity on the right side (arrow).
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F1
Atrophy of both shoulder girdles was observed (Figure 1).
Motor nerve conduction study (NCS). An initial NCS (A,B) shows a reduced amplitude of compound muscle action potentials (CMAPs) of the left musculocutaneous nerve (A: 1.1 mV, recording of the biceps brachii muscle) and left axillary nerve (B: 0.5 mV, recording of the deltoid muscle). A 1-month follow-up NCS (C-E) shows the improved amplitude of CMAPs of the left axillary nerve (C: 10.2 mV), the left musculocutaneous nerve (D: 13 mV), and a conduction block of the left radial nerve (recording of the extensor indicis muscle) between the elbow and spiral groove (E). A 5-month follow-up NCS (F) reveals a persistent conduction block of the left radial nerve.
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F2
An initial nerve conduction study (NCS), performed 2 months after symptom onset, showed a decrease of compound muscle action potential amplitude in the left musculocutaneous nerve (Figure 2A, recording of the biceps brachii muscle) and axillary nerve (Figure 2B, recording of the deltoid muscle) and a significant asymmetry of sensory nerve action potentials of the left lateral antebrachial cutaneous nerve (2.0 muV) compared to the right side (5.0 muV). In the follow-up study of the left axillary (Figure 2C) and musculocutaneous (Figure 2D) nerves 4 weeks after the initial study, the amplitude of compound muscle action potential was improved. However, on the conduction study of the left radial nerve that was not included in the initial study, we detected a conduction block between the spiral groove and the elbow (Figure 2E, recording of the extensor indicis muscle). A 5-month follow-up NCS revealed a persistent conduction block of the left radial nerve (Figure 2F).
Ultrasound images from cine clips of the left radial nerve in the short axis show a normal posterior interosseous fascicle (arrowhead) within the radial nerve (A), swelling (arrowhead) is noted as the nerve is traced proximally (B), followed by fascicular constriction (arrow) (C), and a swollen fascicle (arrowhead) proximal to the constriction (D). Intraoperative photograph shows partial constriction (E) of radial nerve before branching posterior interosseous and superficial radial sensory nerves proximal to the lateral epicondyle. After neurolysis, constriction (F) of the posterior interosseous fascicle was discovered.
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F3
A 4-week follow-up ultrasound revealed constriction of the left posterior interosseous fascicle within the left radial nerve at 1.5 cm proximal to the lateral epicondyle (Figures 3A-D). Surgical exploration was performed 6 months after symptom onset and confirmed fascicular constriction at the area identified by ultrasound, for which interfascicular neurolysis was performed (Figures 3E,F).