308 - Anterior Interosseous Nerve (AIN) Lesions or Syndrome: A Case Report

Thursday, February 22, 2024

5:00 PM – 6:30 PM EDT

Co-Author(s)

MD

Miguel DeMarzo, III, MPH

OMS IV
Kansas City University
Oklahoma City, Oklahoma, United States
JP

Jennifer T. Pham, DO

Resident Physician PGY1
Baylor Scott and White All Saints Medical Center
Carrollton, Texas, United States

Presenting Author(s)

DK

Daniel Khokhar, BS

OMS IV
VCOM-Carolinas
Davenport, Florida, United States

Co-Author(s)

OS

Omar Selod, DO

Attending Physician
PMR Fort Worth
Fort Worth, Texas, United States

Case Diagnosis: Anterior Interosseous Nerve (AIN) Lesion or Syndrome

Case Description: A 43 year old male presented with weakness of his right thumb ongoing for three months. At work, he was using a downward thrust motion when his right hand slipped off and started feeling stiff. He reports progressive inability to hold items in his right hand and having to modify daily activities. Denies paresthesias in the right hand. Pertinent physical exam findings included weakness of right flexor pollicis longus and flexor digitorum profundus at the second digit. Okay sign was positive on the right with difficulty flexing the right thumb interphalangeal joint. MRI performed two weeks prior to electrodiagnostic evaluation was unremarkable. Electrodiagnostic findings were significant for decreased recruitment of the pronator quadratus, and NCS findings of decreased amplitude on proximal stimulation of median motor nerve, which suggest an anterior interosseous nerve (AIN) lesion. Electrodiagnostic results were sent to the hand surgeon for further management.

Discussions: The patient’s inability to form an ‘O’ due to lack of right thumb interphalangeal flexion included a differential of a ligamentous finger lesion or a motor mononeuropathy. Based on this patient’s physical exam, acute findings on electrodiagnostic studies, and a negative MRI, an AIN compression lesion is more likely. Anterior interosseous nerve lesion or syndrome (AIN) is rare and only documented to comprise less than 1% of all upper extremity neuropathies. The suspected etiology in this case was from his employment as a mechanic, leading to hypertrophy of the pronator muscles.

Conclusions: Because AIN syndrome is a rare neuropathy, the history, physical exam, and electrodiagnostics are instrumental to reaching our final diagnosis. With the prevalence of pure AIN lesions being so low, reports are needed to further understand possible etiologies.