Hourglass-like fascicular constriction of the median nerve: case series

Background. The anterior interosseus nerve (AIN) syndrome is a rare pathology, with cause is discussed. The findings in isolated AIN patients are in the main trunk of median nerve. It is confirmed by neuroimaging data and intraoperative picture in the form of the construction of fascicles in the nerve.

Aim. To describe the clinical and instrumental characteristics of patients with isolated non-traumatic lesion of AIN.

Materials and methods. The clinical, electrophysiological and neuroimaging data of 7 patients with isolated nontraumatic lesion of AIN were retrospectively analyzed, three of whom underwent surgical treatment.

Results. All patients complained of neuropathic pain in the affected upper limb, with an average intensity of 8 points according to visual analog scale and a duration of 1.5 to 4 weeks. Weakness of the flexor pollicis longus from 1 to 3 points on the MRC (Medical Research Council Weakness) scale was observed in all cases, weakness of flexion of the distal phalanx of the index finger in 6 patients from 1 to 3 points, which indicated an isolated lesion of the anterior interosseous nerve.

Needle electromyogram revealed denervation in c in all cases, 5 patients – in the pronator teres.

The fascicular constriction from 1 or 2 sections of the median nerve were detected at the shoulder level on the affected side by ultrasound in 6 patients. An increase in the cross-sectional area of the median nerve at the shoulder level in 2 cases we observed, in one case the changes were o bilateral and asymmetric. In 2 cases, an increase in cross-sectional area of С₅ root was noted on the affected side by no more than 23 % of the normal value. A change in echogenicity and size decrease of the pronator quadratus, when compared with the opposite side, was noted in all cases.

Conclusion. Patients with isolated AIN syndrome needs intensive evaluation to identify the localization of the level of damage to the median nerve.

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