Page 346 - Medicine and Surgery

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342 Chapter 7: Nervous system

nerves repaired or grafted if possible. Pain relief may be Table 7.15 Causes of carpal tunnel syndrome
required.
Hormonal Pregnancy, oral contraceptive pill,
periods, hypothyroidism,
Median nerve lesions diabetes mellitus, acromegaly
Peripheral Oedema Cardiac failure
Definition Mechanical/degenerative Fractures of the lunate,
rheumatoid arthritis
The median nerve arises from the brachial plexus and
supplies the flexor aspect of the forearm and the follow-
ing short muscles of the hand (LOAF) – the Lateral two
Aetiology
lumbricals, Opponens pollicis, Abductor pollicis brevis
Often idiopathic (for other causes see Table 7.15).
and Flexor pollicis brevis).
Pathophysiology
Aetiology/pathophysiology
The carpal tunnel is a tight space through which all the
Mediannerveinjuriestendtooccurnearthewristorhigh
tendons to the hand and the median nerve pass. Any
up the forearm. Where the median nerve passes through
cause of swelling is therefore likely to cause compres-
the anterior cubital fossa under the biceps aponeurosis
sion of the medial nerve. The condition is commonly
into the forearm it is vulnerable to damage by forearm
bilateral.
fractures and elbow dislocations (high lesions). It then
passes under the flexor retinaculum (through the carpal
tunnel) into the hand – low lesions are caused by com- Clinical features
Tingling and numbness in the thumb, index finger and
pression in carpal tunnel syndrome (see below), cuts to
middle finger. Characteristically the pain wakes the pa-
the wrist or carpal dislocation.
tient at night and the patient shakes the wrist or hangs
it over the side of the bed to relieve symptoms (unlike
Clinical features
in cervical spondylosis). Symptoms are also induced by
Low lesions: There is loss of muscle bulk in the thenar

repetitive actions, or when the wrists are held flexed for
eminence, abduction and opposition of the thumb are
sometime,forexamplewhilstknittingorreadinganews-
weak and sensation is lost over the radial three and a
paper, and this latter can be used as a test (Phalen’s test),
half digits on the palmar surface.
withthewristhyperflexedfor1–2minutes.Alternatively,
High lesions: In addition to the clinical findings of a

tapping on the carpal tunnel (Tinel’s sign) may repro-
low lesion, the long flexors of the thumb, index and
middle fingers are paralysed. duce the symptoms although both tests are unreliable.
Usually the dominant hand is affected first, but the con-
dition is normally bilateral.
Management
If the nerve is severed suture or grafting should be at- Clumsiness and weakness may occur in late cases,
when there is often wasting of the thenar eminence and
tempted.
decreased palmar sensation.
Carpal tunnel syndrome
Investigations
Definition Median nerve conduction studies show impaired con-
Syndrome of compression of the median nerve as it duction at the wrist.
passes under the flexor retinaculum.
Management
Age Splinting the wrist in extension, particularly at night is
Usually 40–50 years. usefulpriortosurgery,duringpregnancy,orinthosewho
wishtoavoidsurgery.Diureticsmayhelp.Corticosteroid
Sex injection provides temporary relief. Definitive treatment
F > M (8:1) is by surgical division of the flexor retinaculum, usually