PicoBlog

A 62-year old male come to A&E on a Sunday morning with a dropped wrist. What is the diagnosis? 

This is typically due to compression of the radial nerve as it winds around the humerus in the spiral groove of the humerus. It often occurs in association with excessive drinking or the use of sedatives. It is typically associated with weakness in all radial nerve muscles with wrist, thumb, and finger drop. Recovery is usual but can take up to six months.

Please be aware that a Saturday night palsy is often a manifestation of alcohol or substance misuse, which should be looked for and managed accordingly. What are the clinical signs of acute and chronic alcohol misuse? Are there any blood tests you can do to confirm the clinical findings?

Don’t assume a radial nerve palsy is a Saturday night palsy as it may be part of a mononeuritis multiplex and hence a full neurological examination is required. A mononeuritis multiplex is when multiple single nerves are involved and typically due to systemic vasculitis, infections or infiltrative conditions. 

In the past painters used to develop wrist drop; it was referred to as a Painter’s palsy. Do you know why it occurred and why we don’t see it anymore? 

A high radial nerve palsy involves the radial nerve proper, whereas the low palsy involves the posterior interosseous nerve (PIN) (both of these are near the level of the elbow). The importance in differentiating a high from low radial nerve palsy is in the presence or absence of active wrist extension.

High radial nerve:

Triceps brachii (C6,7,8)

Anconeus (C6,7,8)

Brachioradialis (C5-6)

Extensor carpi radialis longus (C6-7)

Deep branch of the radial nerve:

Extensor carpi radialis brevis (C6-7)

Supinator (C5,6,7)

Posterior interosseous nerve (a continuation of the deep branch after the supinator):

Extensor digitorum (C7,8)

Extensor digiti minimi (C7,8)

Extensor carpi ulnaris (C7,8)

Abductor pollicis longus  (C7,8)

Extensor pollicis brevis  (C7,8)

Extensor pollicis longus  (C7,8)

Extensor indicis (C7,8)

It is important to test the sensory loss and differentiated radial nerve, from C8 root loss. 

The reflexes that are depressed or lost with radial nerve palsy are triceps, brachioradialis and supinator reflexes. Please be aware that the biceps jerk, which is from the musculocutaneous nerve (C5-6), can look very brisk as a result of a weak triceps, i.e. it is unopposed as it has lost its antagonist. 

What other non-cranial mononeuropathies should you know about?

This list is limited to nerves with both sensory and motor components. Can you generate a list of sensory mononeuropathies that are important to know about? 

This case illustrates why you need to know your neuroanatomy to be competent at assessing neurological cases.

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General Disclaimer: Please note that the opinions expressed here are those of Professor Giovannoni and do not necessarily reflect the positions of Barts and The London School of Medicine and Dentistry nor Barts Health NHS Trust. 

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