Carpal tunnel syndrome in athletes

Numbness and tingling in the fingers at night, weakness of grip, clumsiness of small movements are typical signs of carpal tunnel syndrome. In athletes, it is provoked by repeated stress on the wrist, oedema and, which is often kept silent, hormonal drugs, primarily growth hormone. The editors analyze why the median nerve is compressed and how pharmacology can be involved.

Anatomy of the carpal tunnel

The carpal tunnel is a narrow tunnel on the palmar surface of the wrist. Its bottom and walls form the bones of the wrist, and the "roof" is a dense transverse ligament. Through this tunnel pass nine tendons of the flexors of the fingers and the median nerve, which provides sensitivity to the thumb, index, middle and half of the ring finger, as well as the movement of some muscles of the thumb.

The channel has rigid walls and practically does not stretch. Therefore, any increase in the volume of its contents — swelling of tendon sheaths, fluid retention, tissue thickening — increases the pressure inside and compresses the nerve. First, the blood supply to the nerve is disturbed, which gives intermittent symptoms, and with prolonged pressure, damage to its sheath and fibres develops.

Carpal tunnel syndrome is the most common tunnel neuropathy. A population-based study by Atroshi et al (1999) in Sweden estimated its prevalence among adults to be approximately 3–4%, depending on criteria. Women get sick more often, the peak occurs in middle age, but athletes and people with physical labor have their own specific risks.

Typical symptoms described in the review by Padua et al. (2016): numbness, tingling and burning in the zone of innervation of the median nerve, which increase at night and make you "shake" the hand; pain that may radiate to the forearm; clumsiness and objects falling out of hands. In the later stages, atrophy of the muscles of the thumb increases.

Sports and general risk factors

In sports, the carpal tunnel is most affected by repetitive bending and extension of the wrist under load, a long grip and direct pressure on the base of the palm. This is typical for cycling (steering wheel support), rock climbing, rowing, weightlifting and crossfit, wheelchair athletes, as well as tennis, golf and badminton.

• Mechanical: prolonged wrist extension under weight (push-ups, front squats), bar grip, steering wheel pressure.
• Traumatic: fractures of the radial bone, dislocations of the wrist bones, tendosynovitis of the flexors.
• Metabolic and endocrine: diabetes, hypothyroidism, acromegaly, obesity.
• Fluid retention: pregnancy, kidney failure, hormonal drugs.
• Inflammatory: rheumatoid arthritis and other arthritis.

Cyclists often experience numbness in their hands after long rides. More often, the ulnar nerve in Guyon's canal (pinky and ring finger) is affected, but compression of the median nerve also occurs. The distribution of symptoms helps to distinguish between them: the median nerve is "responsible" for the first three fingers.

In strength athletes, an additional factor is hypertrophy of the muscles of the forearm and tendons, as well as the frequent use of wrist bandages, which, when tightened too tightly, increase the pressure on the tissues. Large volumes of grip work without sufficient recovery contribute to tendosynovitis — inflammation of tendon sheaths.

We will separately mention general medical conditions. Hypothyroidism and diabetes in themselves increase the risk of neuropathies, and they may go undiagnosed in athletes. If the symptoms are bilateral and appeared without obvious overload, the doctor will definitely check these reasons.

Growth hormone and IGF-1

Growth hormone has the clearest pharmacological connection with carpal tunnel syndrome. In the official instructions for somatropin drugs, carpal tunnel syndrome, swelling, pain in the joints and muscles are listed among the side effects, especially in adults. The mechanism is associated with sodium and fluid retention, as well as soft tissue swelling.

Liu et al.'s (2008) systematic review on the effects of growth hormone on athletic performance noted that fluid retention, soft tissue swelling, arthralgia, and carpal tunnel syndrome were more common in healthy individuals receiving the drug. At the same time, the researchers did not find convincing evidence of improvement in sports results.

Acromegaly — a disease with a chronic excess of one's own growth hormone — provides an even clearer model. A review by Melmed (2006) describes carpal tunnel syndrome as one of the common manifestations of acromegaly, along with thickening of the soft tissues of the hands and feet, joint pain and sweating. Long-term excessive use of growth hormone can reproduce certain features of this condition.

Growth hormone-stimulating peptides and IGF-1 preparations may theoretically have similar effects, but high-quality clinical data on their safety in healthy individuals are scarce. They are all on the WADA Prohibited List, and black market products often have unknown ingredients and dosages.

Steroids, fluid retention and other drugs

Anabolic-androgenic steroids are rarely directly associated with carpal tunnel syndrome. However, supraphysiological doses can cause sodium and water retention, especially with high oestrogen levels, and rapid weight and strength gains increase the mechanical load on the hands. A scientific statement from the Endocrine Society (Pope et al., 2014) describes fluid retention as a possible side effect.

Insulin and insulin-like states are also important indirectly. Diabetes increases the vulnerability of nerves to compression, and at the beginning of insulin therapy, diabetic patients sometimes experience swelling. If an athlete uses insulin outside of medical prescription, it adds to the risk of neuropathy and fatal hypoglycaemia.

Among the legal drugs, it is worth mentioning some hormonal contraceptives and hormone replacement therapy in women, which can contribute to fluid retention, as well as aromatase inhibitors: joint pain and hand complaints, in particular tendosynovitis, have been described in women treated for breast cancer. Athletes are not prescribed these drugs without medical indications.

It is important to understand that a pharmacological cause does not exclude a mechanical one. Most often, symptoms appear where several factors are combined: intensive grip training, swelling on the background of drugs and insufficient recovery. Therefore, prevention should be comprehensive.

Editorial conclusions

Carpal tunnel syndrome occurs when pressure in the rigid carpal tunnel builds up and compresses the median nerve. In athletes, the main mechanical factors are repeated loads on the grip and wrist extension.

Growth hormone has the clearest pharmacological connection: fluid retention, oedema, and carpal tunnel syndrome are described in instructions and systematic reviews. Steroids, oestrogens, and other agents can contribute to fluid retention.

Numbness of the fingers at night, weakness of the grip and objects falling out of the hands are reasons to consult a doctor and honestly tell about all the drugs used.

The editors recommend also reading our materials on the prevention and diagnosis of carpal tunnel syndrome, on the side effects of growth hormone and on fluid retention against the background of hormonal drugs.

List of used literature

1. Padua L, Coraci D, Erra C, et al. Carpal tunnel syndrome: clinical features, diagnosis, and management. Lancet Neurol. 2016;15(12):1273–1284.
2. Atroshi I, Gummesson C, Johnsson R, et al. Prevalence of carpal tunnel syndrome in a general population. JAMA. 1999;282(2):153–158.
3. Liu H, Bravata DM, Olkin I, et al. Systematic review: the effects of growth hormone on athletic performance. Ann Intern Med. 2008;148(10):747–758.
4. Melmed S. Acromegaly. N Engl J Med. 2006;355(24):2558–2573.
5. Pope HG Jr, Wood RI, Rogol A, et al. Adverse health consequences of performance-enhancing drugs: an Endocrine Society scientific statement. Endocr Rev. 2014;35(3):341–375.
6. U.S. Food and Drug Administration. Genotropin (somatropin) for injection: prescribing information. Silver Spring, MD: FDA.
7. World Anti-Doping Agency. The World Anti-Doping Code: International Standard — Prohibited List. Montreal: WADA; оновлюється щороку.