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

Discussion

Answer:  anterior interosseous nerve syndrome

Findings:

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

Discussion:

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.
  
  
  
  

References:

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