If 2 or more nerves are affected it is called mononeuritis multiplex. Causes may be remembered by the mnemonic DRAWS PLC:
- leprosy/lyme disease
- carcinomatosis/churg strauss
Important individual mononeuropathies to be familiar with include:
Key nerves of the arm: RUM - radial nerve C5-T1, ulnar never C6-T1 and median nerve C7-T1
- Origin: C5-T1
- Route: radial groove in humerus then anterior to the lateral epicondyle
- Sensory supply: lateral 3.5 fingers in back of hand; only small area at base of thumb unique
- Motor supply: tricipes and extensors of wrist/fingers plus suppinators
- Classical presentation: 'Saturday night paralysis' - fall asleep with arm across back of chair, compress radial nerve in its groove and bruise it so awake with wrist drop.
- Origin: C6-T1
- Route: posteriomedial aspect of humerus then adjacent to ulna. Runs superficial to flexor retinaculum into hand.
- Sensory supply: medial 1.5 fingers
- Motor supply: interossei, hypothenar eminence, medial 2 lumbicals
- Classical presentation: claw hand/unable to cross fingers
- Origin: C7-T1
- Route: medially, goes through carpal tunnel
- Sensory supply: lateral 3.5 fingers palmar aspect of hand plus nail beds of these fingers
- Motor supply: pronator, LOAF = 1st and 2nd lumbricals, opponens pollicis, abductor pollicis brevis, flexor pollicis brevis (=thenar enimence)
- Classical presentation: carpal tunnel syndrome
Carpal Tunnel Syndrome is so common it deserves its very own battle...