Weekly Case

Title : Case 621

Age / Sex : 50 / F

Chief complaint : she felt weakness in left hand after a pilates class 3 months ago

What is your diagnosis?

Two weeks later, you can see the final diagonosis with a brief discussion of this case (Please submit only one answer).

Courtesy : 
Sun-Young Park, Hallym Sacred Heart Hospital


Answer:  anterior interosseous nerve syndrome



T2 high SI with enhancment and atrophy at flexor pollicis longus, radial part of the flexor digitorum profundus, and pronator quadrates (Anterior interosseous nerve denervation muscles) of left elbow. No evidence of mass along the median nerve and anterior interosseous nerve.
-> Anterior interosseous nerve syndrome.


Differential Diagnosis:

  • Carpal tunnel syndrome

  • Pronator teres syndrome



Anatomy of anterior interosseous nerve

  • Arises from the median nerve just distal to the elbow

  • Location distal to the typical of lesions that cause pronator syndrome

  • Pure motor nerve

  • Supplies radial half of the flexor digitorum profundus (FDP), flexor pollicis longus (FPL), and the protator quadraqus (PQ) muscles

  • Anterior interosseous nerve (AIN) syndrome

  • Entrapment or compression of the anterior interosseous nerve in the proximal part of the forearm.

  • Cause: direct traumatic damage and external compression

  • Clinical findings:

    • Pronation weakness due to weakness of the pronator quadrates muscle

    • Pinching deformity (circle sign positive) that is due to weakness of the thumb and index finger.

    • Dull pain in the volar aspect of the forearm, combined with an acute onset of muscle weakness (no sensory change).

  • MRI findings

    • Edema or atrophy of FDP, FPL, PQ muscles.

    • Edema in the pronator quadrates muscle – the most reliable sign.



Kim SJ, Hong SH, Jun WS, et al. MR imaging mapping of skeletal muscle denervation in entrapment and compressive neuropathies. Radiographics, 2011;31(2):319-332

Andreisek G, Crook DW, Burg D, Marincek B, Weishaupt D. Peripheral neuropathies of the median, radial, and ulnar nerves: MR imaging features. Radiographics 2006;26:1267-87

Correct Answer
Total applicants 30 Correct answers 28
Name Institution
윤유성 순천향대 부천병원, 전문의
김기욱 국군대전병원, 전문의
이진영 전문의
이혜란 전문의
신재환 국군춘천병원, 전문의
최형인 국군수도병원, 전문의
김유진 전문의
김창현 전문의
이승은 전문의
장성원 중앙보훈병원, 전공의
김동수 전공의
이규정 고대안암병원, 전문의
권소이 전문의
김지은 서울대학교병원, 전문의
박병진 국군강릉병원, 전문의
한진우 전공의
손상욱 군의관, 전문의
권영호 경희의료원, 전문의
이준영 전공의
강지희 서울대학교병원, 전문의
조은경 새움병원, 전문의
전인환 전문의
안준형 공중보건의, 전공의
김보람 전문의
송윤아 전문의
한유비 병무청, 전문의
김형민 전문의
조영민 전문의