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ANTERIOR INTEROSSEOUS NERVE PALSY

Introduction

The anterior interosseous nerve (AIN) is a branch of the median nerve and is principally a motor nerve. AIN palsy, also known as Kiloh-Nevin syndrome,1 is a rare syndrome characterized by complete or partial loss of motor function of the flexor pollicis longus (FPL), flexor digitorum profundus (FDP), and pronator quadratus (PQ). The symptoms include difficulty with writing and activities that require pinching motions of the index finger with the thumb. Sometimes, the middle finger also may be affected. Patients may report dull pain in the proximal forearm that gets aggravated with activity, but there is no loss of sensation.2-4

Pathophysiology

  • It is still debated whether AIN palsy is a neuritis, compression neuropathy, or both
  • In rare cases, an anatomical variant of FPL, the Gantzer muscle, can be a cause
  • There are other potential anatomic, inflammatory, infectious, posttraumatic, and compressive causes
  • AIN palsy is often triggered by viral illness and/or immunizations 3

Related Anatomy

  • Median nerve
  • Anterior interosseous nerve
  • FPL
  • Radial half of FDP
  • PQ
  • Lacertus fibrosus
  • Flexor digitorum superficialis sling

Incidence and Related Conditions

  • Incidence of AIN palsy is rare, accounting for <1% all upper-extremity peripheral neuropathies

Differential Diagnosis

  • Parsonage-Turner syndrome
  • Flexor tendon rupture or muscle rupture (Mannerfelt syndrome)
  • Flexor tendon adhesion, stenosing or adhesive tenosynovitis
  • Peripheral neuropathy
  • Pronator teres syndrome
  • Carpal tunnel syndrome
ICD-10 Codes

  • ANTERIOR INTEROSSEOUS NERVE PALSY

    Diagnostic Guide Name

    ANTERIOR INTEROSSEOUS NERVE PALSY

    ICD 10 Diagnosis, Single Code, Left Code, Right Code and Bilateral Code

    DIAGNOSISSINGLE CODE ONLYLEFTRIGHTBILATERAL (If Available)
    ANTERIOR INTEROSSEOUS NERVE PALSY (MEDIAN NERVE) G56.12G56.11G56.13

    ICD-10 Reference

    Reproduced from the International statistical classification of diseases and related health problems, 10th revision, Fifth edition, 2016. Geneva, World Health Organization, 2016 https://apps.who.int/iris/handle/10665/246208

Clinical Presentation Photos and Related Diagrams
  • AIN Palsy Sign with absent index DIP and thumb IP flexion
    AIN Palsy Sign with absent index DIP and thumb IP flexion
  • AIN Palsy Sign
    AIN Palsy Sign
  • Normal Index FDP and FPL
    Normal Index FDP and FPL
Symptoms
Dull pain in the forearm and/or elbow
Weakness in the thumb, index finger and sometimes the middle finger
Difficulty with pinching movement and pinching strength
Typical History

A typical patient is a middle-aged male or female working in an office. Patients initially complain about a vague pain in the proximal forearm and difficulty with writing, knitting, and other activities that require a pinching grip. Patients do not experience any abnormal tingling or prickling sensation. Patients might have suffered a viral illness before experiencing pain in the forearm.  Patient's history negative for rheumatoid arthritis.

Positive Tests, Exams or Signs
Work-up Options
Treatment Options
Conservative
  • Observation for 6–18 months for patients with suspected spontaneous, neuropathic AIN palsy
  • High dose of corticosteroids and antiviral medications such as acyclovir3
Operative
  • Nerve exploration and neurolysis in patients with no electrodiagnostic evidence of recovery after 7–10 months of observation
Treatment Photos and Diagrams
  • Anterior elbow incision has exposed the lacertus fibrosus
    Anterior elbow incision has exposed the lacertus fibrosus
  • The lacertus fibrosis has been open exposing the cephalic vein, basilic vein and the median nerve.
    The lacertus fibrosis has been open exposing the cephalic vein, basilic vein and the median nerve.
  • The dissection has moved deeper exposing: 1. Median Nerve, 2. Median Nerve branch to the Pronator Teres, 3. retracted Pronator Teres, 4. Flexor Digitorum Superficialis muscle after transection of the fascial sling, 5. Anterior Interosseous Nerve with color change from compression.
    The dissection has moved deeper exposing: 1. Median Nerve, 2. Median Nerve branch to the Pronator Teres, 3. retracted Pronator Teres, 4. Flexor Digitorum Superficialis muscle after transection of the fascial sling, 5. Anterior Interosseous Nerve with color change from compression.
Complications
  • Current thinking, guided by clinical evidence, is that AIN palsy is a transient idiopathic nerve dysfunction similar to Parsonage-Turner syndrome and not a compression neuropathy that benefits from surgery.
Outcomes
  • Most patients recover completely after 6 weeks to 12 months from the onset of symptoms without surgical intervention
Key Educational Points
  • Current thinking, guided by clinical evidence, is that AIN palsy is a transient idiopathic nerve dysfunction similar to Parsonage-Turner syndrome and not a compression neuropathy that benefits from surgery.
  • Kiloh-Nevin sign: inability to make an “OK” sign with the thumb and index finger
  • Patients with AIN palsy will have a negative flexor pollicis manual compression test
References

Cited

  1. Kiloh LG, Nevin S. Isolated neuritis of the anterior interosseous nerve. Br Med J 1952;1(4763):850–2. PMID: 14916168
  2. Chi Y, Harness NG. Anterior interosseous nerve syndrome. J Hand Surg 2010;35(12):2078–80. PMID: 20961706
  3. Strohl AB, Zelouf DS. Ulnar Tunnel Syndrome, Radial Tunnel Syndrome, Anterior Interosseous Nerve Syndrome, and Pronator Syndrome. J Am Acad Orthop Surg 2017;25(1):e1–10. PMID: 27902538
  4. Rodner CM, Tinsley BA, O’Malley MP. Pronator syndrome and anterior interosseous nerve syndrome. J Am Acad Orthop Surg 2013;21(5):268–75. PMID: 23637145

New Papers

  1. Rodner CM, Tinsley BA, O'Malley MP.Pronator syndrome and anterior interosseous nerve syndrome. J Am Acad Orthop Surg 2013;21(5):268-75. PMID: 23637145

Reviews

  1. Strohl AB, Zelouf DS. Ulnar Tunnel Syndrome, Radial Tunnel Syndrome, Anterior Interosseous Nerve Syndrome, and Pronator Syndrome. J Am Acad Orthop Surg 2017;25(1):e1-e10. PMID: 27902538
  2. Chi Y, Harness NG. Anterior Interosseous Nerve Syndrome. J Hand Surg Am 2010;35(12):2078-80. PMID: 20961706
  3. Koo JT, Szabo RM. Compression Neuropathies of the Median Nerve. J ASSH 2004;4(3):156-175.

Classic

  1. Kiloh LG, Nevin S. Isolated neuritis of the anterior interosseous nerve. Br Med J 1952;1(4763):850–2. PMID: 14916168
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