What is Radial Neuropathy

Radial neuropathy is a type of mononeuropathy which results from acute trauma to the radial nerve that extends the length of the arm.

What is involved?

Radial Nerve

Location

• Most frequently at the Spiral Groove of the humerus
• Could be at the Axilla (Saturday Night palsy)
• Or in the Forearm (Posterior Interosseous Syndrome)

Common symptoms

• Wrist drop, patient unable to extend wrist or fingers up
• Almost always unilateral
• No associated pain
• Occasional forearm/hand/thumb numbness
• Symptoms always present, no night/day preference

Onset

• Sudden
• Usually happens upon waking up one morning
• Or, after a “Saturday Night” at the bar falling asleep with arm hanging over back of chair
• Or following prolonged sitting in a position with arm leaning against sharp object
• Or following misplaced intramuscular injection in the vicinity of the Radial nerve

Risk factors

• No gender preference
• Diabetes or family history of Diabetes
• Alcoholism
• Leaning on arms/axilla, sleeping in wrong position or with somebody leaning on arm
• Trauma

Exam

When first seen, weakness but no atrophy – Wrist drop with inability to extend wrist, fingers.

Always check the three following muscles:

1. Triceps: Ask subject to extend elbow
2. Brachio-Radialis: Ask subject, with thumb pointing to ceiling, to flex forearm. Make sure the belly of the Brachio-Radialis is easily visible (compare to healthy side)
3. Extensor Indicis Proprius: With hand flat on bed, ask subject to raise index finger up

Additional findings:

• Occasional numbness/decreased sensation over dorsum of hand/thumb area
• Difficulty spreading fingers (pseudo-ulnar interosseii weakness)
• Pseudo-Ulnar weakness correctible when wrist held level with forearm by examiner
• Positive Tinel sign (tingling upon tapping nerve) at the humeral Spiral Groove when lesion at that location

Localization

Three possible locations determined by exam of Triceps, Brachio-Radialis and Extensor Indicis Proprius:

• Axilla: Triceps, Brachio-Radialis and Extensor Indicis Proprius all weak, normal to decreased sensation over dorsum hand/thumb area
• Humeral Spiral Groove: Triceps strength is normal, weak Brachio-Radialis (can barely see belly of muscle) and weak Extensor Indicis Proprius, normal to decreased sensation over dorsum hand/thumb area
• Forearm (Posterior Interosseous Syndrome): Triceps and Brachio-Radialis normal, Extensor Indicis Proprius weak, normal sensation over dorsum hand/thumb area

EMG

EMG is very good for localization (Axilla, Spiral Groove, Forearm) and for prognostic value.

Prognostic Value

• In pure myelin lesions (conduction block): recovery may occur after three weeks to a month
• In moderate/severe axonal lesions: recovery may take from 6 months to a year
• In mixed lesions: somewhere in between

Findings

• Slowing, drop in Extensor Indicis Proprius amplitude across compression area in myelin lesions
• Diffuse drop in Extensor Indicis Proprius amplitude with or without slowing in axonal lesions
• Mixture of above in mixed lesions
• Radial sensory spared only in forearm (posterior interosseous) lesions

Recommendations

• Symptomatic treatment
• Stop/decrease cause
• Wrist/finger splint to keep fingers extended in moderate to severe axonal lesions
• Passive wrist, fingers Range of Motion to maintain mobility

What else could it be?

• If other nerves involved, could be Brachial Plexus lesion (do not make the mistake of diagnosing a superimposed Ulnar neuropathy because the interosseii “appear” weak)
• Bilateral Radial palsies—always look for Lead poisoning
• Very rarely, Myotonic Dystrophy can cause weak, wasted forearms and bilateral wrist drop