Disorders of Peripheral Nerves Flashcards
What are the features of a radial nerve palsy?
Weakness of extension of the wrist and fingers, often precipitated by sleeping in abnormal postures, e.g. arm over the back of a chair
Sensory loss over the dorsum of the thumb. Can be associated with diminished triceps reflex
What muscles does the radial nerve supply?
Radial nerve supplies all the arm extensors.
After leaving the brachial plexus it supplies the triceps and extensor carpi radialis.
In the forearm it becomes the posterior interosseous nerve and supplies extensor carpi ulnaris, extensor digitorum and supinator.
A distal lesion of the radial nerve will not always cause a wrist drop, because extensor carpi radialis has already been supplied.
What muscles are innervated by the median nerve?
After leaving the brachial plexus, the median nerve supplies - pronator teres, flexor carpi radialis and flexor digitorum superficialis
It gives off a branch as the anterior interosseous nerve.
The median nerve then passes through the carpel tunnel where it supplies the “LOAF” muscles - lumbricals I and II, opponens policis, abductor pollicis brevis and flexor pollicis brevis
What are the features of a median nerve palsy?
Pain and paraesthesia on palmar aspect of hands and fingers, waking the patient from sleep. Pain may extend to arm and shoulder.
Sensory loss over lateral palm and thumb, index, middle and half 4th finger.
What are the features of an anterior interosseous muscle lesion
This produces weakness of flexor pollicis longus, flexor digitorum profundus I and II, and pronator quadratus.
Palsy of the anterior interosseous nerve causes a hand of benediction and an inability to make an “OK” sign.
What muscles does the ulnar nerve innervate?
There are lots! The easiest way to remember this is that the ulnar nerve innervates all the intrinsic muscles of the hand that are not innervated by the median nerve.
What are the features of an ulnar neuropathy?
At the elbow, this causes paraesthesia on medial border of the hand, wasting and weakness of hand muscles.
All small muscles of the hand excluding abductor pollicis brevis are affected.
Sensory loss over medial palm and little finger and medial half 4th finger.
What is multifocal motor neuropathy with conduction block?
This is a form of chronic inflammatory demyelinating peripheral neuropathy CIDP. Sensory, motor or autonomic nerves can be involved, but the signs are predominantly motor. Multifocal motor neuropathy (MMN) is a variant with only motor involvement.
It presents with features very similar to motor neurone disease, but the nerve conduction studies are diagnostic. They show segmental demyelination and conduction block (areas of demyelination where the signal cannot pass).
It is am important differential diagnosis for MND, because it can be treated with immunosuppressive treatment. In fact MMN is best treated with IVIg.
What are the features of axonal and demyelinating neuropathies on nerve conduction studies?
Demyelinating = decreased nerve conduction velocity but normal amplitude
Axonal = decreased amplitude
