Kiloh-Nevin syndrome / anterior interosseous nerve syndrome

Case contributed by Dr Sören Peters


A 55 year old male presented to the surgery outpatient service with weakness of thumb and index finger flexion of the right hand after previous shoulder surgery a few months prior. History was significant for Leriche syndrome with stent implantation. Clinical examination revealed an inability to form an "O" (or "O.K."-sign) with his right thumb and index finger, i.e. a weakness of flexion of the distal joints, indicating a lesion of the flexor pollicis longus and digitorum profundus muscles. No other pathological findings were noted. An external ultrasound exam of the right forearm had shown intact tendons, but an unspecified "edema of the flexor muscles" (images not available).

Patient Data

Age: 55 years
Gender: Male

A MRI (1,5 T) of the right forearm was ordered: axial T1 TSE, PD fat sat, T1 TSE fat sat after iv gadolinium; coronal T2 STIR, T1 TSE fat sat after iv gadolinium.

Axial images best lend themselves to depicting forearm anatomy (and pathology). T1 TSE revealed no abnormalities. PD (figs. 1-3) and T1 TSE fat sat after iv gadolinium  (figs. 4-6) revealed significant hyperintense signal changes in the flexor pollicis longus (FPL), flexor digitorum profundus (FDP) and pronator quadratus (PQ) muscles; the FDP showed a relative sparing of its ulnar aspect.

Case Discussion

The patient presented clinically with a Kiloh-Nevin or anterior interosseus nerve syndrome. MRI confirmed the clinical findings, revealing denervation-induced edema of the flexor pollicis longus (FPL) , flexor digitorum profundus (FDP) and pronator quadratus (PQ) muscles; typically, only the radial aspect of the FDP was affected.

The median nerve is prone to entrapment syndromes, the best-known of which is carpal tunnel syndrome. Two other distinct entities are pronator teres syndrome and anterior interosseous nerve, or Kiloh-Nevin syndrome.

Etiologically, direct trauma, muscle entrapment or entrapment by fibrous bands, aberrant vessels or adjacent pathology ( e.g. callus, soft tissue masses), and idiopathic are the most common causes; primary nerves tumor are a further, rarer consideration. Differential diagnoses are other entrapment syndromes (often with distinct clinical and neurophysiological findings) and brachial neuroplexitis / Parsonage-Turner syndrome.

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