Radial neuropathy

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

It is known as transient paresthesia when sensation is temporarily abnormal.

Cultural references

There are a number of colloquial terms used to describe radial nerve injuries, which are usually dependent on the causation factor:

• Saturday night palsy from falling asleep with one's arm hanging over the arm rest of a chair, compressing the radial nerve at the spiral groove.
• Honeymoon palsy from another individual sleeping on and compressing one's arm overnight.^[1] This can also refer to anterior interosseous nerve palsy from compression on the forearm resulting in an inability to flex the index and thumb tips.^[2] In this interpretation, it is a branch of the median nerve and not the radial nerve which is affected.
• Handcuff neuropathy from tight-fitting handcuffs compressing the superficial branch of the distal radial nerve; this is also referred to as cheiralgia paresthetica.
• Crutch palsy from poorly fitted axillary crutches.^[3]
• Squash palsy, from traction forces in a manner usually associated with the sport squash, can happen to squash players during prolonged periods between matches.

Presentation

Symptoms vary depending on the severity and location of the trauma; however, common symptoms include wrist drop (the inability to extend the wrist upward when the hand is palm down); numbness of the back of the hand and wrist, specifically over the first web space which is innervated by the radial nerve; and inability to voluntarily straighten the fingers or extend the thumb, which is performed by muscles of the extensor group, all of which are primarily innervated by the radial nerve. Loss of wrist extension is due to paralysis of the posterior compartment of forearm muscles; although the elbow extensors are also innervated by the radial nerve, their innervation is usually spared because the compression occurs below, distal, to the level of the axillary nerve, which innervates the long head of the triceps, and the upper branches of the radial nerve that innervate the remainder of the Triceps. ^[4]

Causes

There are many ways to acquire radial nerve palsy.

The term Saturday Night Palsy refers to an injury to the radial nerve in the spiral groove of the humerus caused while sleeping in a position that would under normal circumstances cause discomfort. It can occur when a person falls asleep while heavily medicated and/or under the influence of alcohol with the underside of the arm compressed by a bar edge, bench, chair back, or like object. Sleeping with the head resting on the arm can also cause radial nerve palsy.

Breaking the humerus and deep puncture wounds can also cause the condition.

Posterior interosseus palsy is distinguished from radial nerve palsy by the preservation of elbow extension.

Prognosis

Radial neuropathy is not necessarily permanent. The majority of radial neuropathies due to an acute compressive event (Saturday night palsy) do recover without intervention. If the injury is demyelinating (meaning only the myelin sheath surrounding the nerve is damaged), then full recovery typically occurs within 2-4 weeks. If the injury is axonal (meaning the underlying nerve fiber itself is damaged) then full recovery may take months or years, or may never occur. EMG and nerve conduction studies are typically performed to diagnose the extent and distribution of the damage, and to help with prognosis for recovery.

References