Carpal tunnel syndrome is relatively common and the vast majority of cases respond well or very well to treatment.
The patient describes numbness or tingling in one or both hands. Classically the pattern of numbness is in the median nerve, affecting the thumb, index, middle and radial border of ring finger.
However, some patients have difficulty distinguishing between which fingers are affected and may say 'all of them'. Symptoms are usually worse at night and patients often wake up in the morning with the numbness. In time they begin to notice difficulty performing particularly dexterous tasks.
If you tap the base of the palm with your index finger the patient may well describe a shower of sparks and tingling in the affected fingers. This is Tinel’s sign. If you press the same area with your thumb for more than 30 seconds, then the patient begins to feel the numbness in the affected areas.
Similarly, Phalen’s test may also provoke the numbness although you often have to perform the test for more than about 30 seconds.
It is possible for symptoms to come from the cervical spine, very rarely at the elbow (the ligament of Struthers) or from a more proximal injury.
Whilst carpal tunnel syndrome is the most common peripheral nerve entrapment syndrome, the second most common is ulnar nerve entrapment behind the medial epicondyle (cubital tunnel syndrome) and this would give numbness in the little finger.
In advanced cases of carpal tunnel syndrome there may also be wasting of the thenar eminence.
Who gets carpal tunnel syndrome?
The condition is more common in women than men. It can occur equally in the left and right hand. It is sometimes provoked by a wrist injury and occasionally a surgeon will perform a carpal tunnel release at the same time as plating a wrist fracture for this reason.
By far the most common association is diabetes mellitus. Diabetes raises the possibility that at least some of the symptoms represent a peripheral neuropathy similar to what we usually see in a patient’s toes and feet but in practice the diabetes seems to increase the risk of carpal tunnel per se and surgery is still effective, perhaps with a slightly higher risk of infection.
There is also an association with rheumatoid arthritis, steroid treatment and hypothyroidism. Some women get carpal tunnel syndrome during pregnancy that resolves after the baby is delivered. In short, the condition seems to be associated with fluid retention and swelling in the wrist from almost any cause.
The investigation of choice is nerve conduction studies. Here, the neurophysiologist attaches electrodes to the patient’s arm and tests the speed of conduction across the carpal tunnel.
However, there is controversy as to whether it is worth requesting nerve conduction studies as the history and physical signs are usually so clear cut.
Quite a lot of people respond to splints that hold the wrist in slight extension. Very often these only need to be worn at night. Splints are cheap and non-invasive.
The next step up is an injection into the carpal tunnel using local anaesthetic and steroid. Several steroids are available and there is no hard evidence that any one of them is any better than any other. I usually warn the patient of just how unpleasant this injection can be.
Probably about half of patients respond to the injection although the effects are often short lived. The steroid suppresses inflammation in the carpal tunnel making the tendons and surrounding soft tissue shrink a little.
If this does not work or if the patient requests surgery, carpal tunnel decompression surgery is a day case procedure and is usually performed under local anaesthetic. Typically the tourniquet time is less than 10 minutes and sometimes less than five minutes. The surgeon makes an incision about 2cm long longitudinally at the base of the palm.
We advise a high arm sling to be worn most of the time for 48 hours after surgery to reduce swelling. After five days the bandage can be taken down. The adhesive dressing should be worn for a full two weeks and the patient has to keep the hand dry for two weeks.
In our unit we do not routinely see carpal tunnel patients for follow up as the response rate to surgery is often over 90%.
There is a theoretical risk of infection but the hand has an excellent blood supply and usually heals well. If infection seems to be occurring it is reasonable to prescribe a suitable antibiotic and take a swab.
About 5 to 10% of patients do not seem to improve. Re-exploration is sometimes performed but in practice the response to re-exploration is more disappointing than first time surgery.
There is a theoretical risk of hitting a cutaneous nerve and having a numb patch over the thenar eminence but this risk is very low.
- Mr Cutts is consultant orthopaedic surgeon at the James Paget Hospital, Norfolk