Introduction
In carpal tunnel syndrome, damage to the median nerve can occur for various reasons. This nerve passes through the middle of the carpal tunnel, whereby the carpal tunnel is also traversed by several muscles or their tendons. It is therefore a bottleneck passage in which the nerve can become trapped. This constriction and the associated pain and sensitivity disorders in the hand area are called carpal tunnel syndrome.
Causes
At this point, the causes and pathogenesis of carpal tunnel syndrome are presented. Although there are many known causes for carpal tunnel syndrome, the cause of its development in individual cases often remains unknown (over 50%). In medical terminology, this is called an idiopathic cause, since it is not known where the sudden sensory disturbances in the hand area come from, or it is unclear why the nerve is suddenly constricted in the carpal tunnel area. Even direct observation of the carpal tunnel during an operation does not change this. Generally speaking, the cause of carpal tunnel syndrome is either a constriction of the median nerve in the carpal tunnel from the outside, or, which is more common, a compression of the nerve by the structures that travel with the nerve through the carpal tunnel.
Known causes of carpal tunnel syndrome
During inflammatory processes, fluid may accumulate in the carpal tunnel. More often, an inflammation of the tendon sheath (synovialitis) of the flexor tendons of the wrist is also the cause. Normally, each muscle is surrounded by a tendon sheath to prevent friction between the individual tendons.
If, however, these tendon sheaths are subjected to strong mechanical stress, they may become inflamed. Musicians in particular often suffer from tendon sheath inflammation, but also athletes, especially handball or basketball players know the problem. The inflammation of the tendon sheaths causes them to swell.
However, since the carpal tunnel is very narrow, there is enormous pressure in the carpal tunnel area. This pressure is transferred to the median nerve that runs through the tunnel. It is increasingly constricted by the swelling of the tendon sheaths and then leads to the classic symptoms of carpal tunnel syndrome.
Also with patients with a rheumatic illness it can come frequently to a carpal tunnel syndrome since the inflammation of the joints can spread and lead thus to a swelling and narrowness within the range of the carpal tunnel, which constricts then again the nervus medianus. Rheumatism is particularly important in this context. One cause of carpal tunnel syndrome can be an anatomical narrowing in the area of the carpal tunnel.
In some patients, the carpal tunnel forms too narrowly during bone growth, for example, which then leads to a constriction of the nerve. Colloquially, one therefore often speaks of a constriction syndrome when describing carpal tunnel syndrome. If this constriction is determined by an anatomical condition, the patient usually notices this in early adolescence when bones and tendons are growing.
Wear in the area of the carpal bones (arthrosis) or bone tumors can also lead to a bony constriction of the carpal tunnel. Fractures close to the carpal can press and constrict the median nerve from the outside due to a remaining malposition after its bony reconstruction. However, even with correct healing, a narrowing of the carpal tunnel can occur, since fractures are usually accompanied by inflammation, which in turn leads to swelling.
Overloading, for example during sports, can also lead to an increase in volume and pressure on the median nerve. There are various hormonal causes that lead to the development of carpal tunnel syndrome. Typically, the median nerve is then hypersensitive to pressure loads.
Since the symptoms of carpal tunnel syndrome are particularly common in women who are in their menopause, it is assumed that water retention and swelling in the area of the carpal tunnel lead to a narrowing of the nerve. Although a woman’s menopause cannot be directly seen as the cause of carpal tunnel syndrome, there seems to be some connection. Tissue swelling can also cause carpal tunnel syndrome during pregnancy, although this should disappear after pregnancy.There are other causes which are suspected to be related to carpal tunnel syndrome, although it is not entirely clear whether the disease is really the cause of the symptoms.
On the one hand, it is suspected that hypothyroidism can lead to carpal tunnel syndrome. Here too, swelling in the area of the carpal tunnel is probably to blame for the narrowing. In addition, a connection between the syndrome and hyperthyroidism is suspected.
A sugar disease (diabetes mellitus) and other metabolic diseases that occur less frequently, such as amyloidosis, mucopolysacharidosis, chondrocalcinosis or gout, can also lead to constriction in the carpal tunnel. In diabetics, increased pressure sensitivity of the median nerve is suspected to be a trigger for carpal tunnel syndrome in the context of polyneuropathy (sugar-related general nerve damage). Other hypotheses assume that worsened blood flow in diabetics is the cause of the swelling in the area of the carpal tunnel and thus responsible for the symptoms. Mucosal sacculations, known as ganglions, can also lead to carpal tunnel syndrome.
