Why is Carpal Tunnel Syndrome Associated with Hypothyroidism?
Carpal tunnel syndrome (CTS) is a result of compression of the median nerve and has a 10% lifetime risk with known occupational associations (Olney 2001). Hypothyroidism is an accepted risk factor for CTS (Solomon 1998). However, what is the mechanism for this? Does the hypothyroidism cause the carpal tunnel symptoms? Or do both conditions share a similar potential aetiology?
Palumbo et al (2000) state that no study clearly defines the nature of the association between hypothyroidism and CTS. In their study Palumbo et al (2000) compared 26 patients (45 hands) with a diagnosis of primary hypothyroidism and CTS. 24 healthy controls (47 hands) were used. They tested sensation, muscle atrophy and weakness, Phalen’s, Tinel’s test and manual compression tests and conducted electrodiagnostic tests on the median nerve. In the control group only clinical tests produced two false positives. In the test subjects 19 patients (31 hands) had CTS symptoms, 16 (25 hands) patients had clinical signs and only 6 patients (7 hands) had electodiagnostic changes. All these patients were biochemically euthyroid, normal function following thyroid treatment. In these patients CTS symptoms and a positive physical examination are more common than expected by the reported sensitivity of electrodiagnostic testing.
Other studies suggest a mechanism for musculoskeletal pain in other areas of the body. Interestingly Schwartz et al (1983) discuss the frequency of the tarsal tunnel syndrome in hypothyroid patients. Although not as frequent the frequency suggests a similar mechanism driving the incidence of both conditions. Similarly, Golding (1970) discusses 9 case histories of hypothyroid patients with complex pain patterns in a combination of the back and, or the upper and, or lower limbs. Notably in one case the pain relieving medication phenylbutazone aggravated symptoms which was attributed to it’s anti-thyroid effect. This weakly suggests that hypothyroidism may be the cause of these distal symptoms.
Furthermore, 75% of hypothyroid patients have a delayed ankle jerk and indicating pseudo-myotonia is common in many of these patients. In addition muscle aches are commonly accepted symptoms of hypothyroidism (Golding 1970). This defect in the reflex arc is not due to the neural components but is thought to be due to defects in contractile mechanism it’s self (Lambert et al 1951).
These musculoskeletal symptoms may all potentially be explained by one common mechanism, the effects of untreated hypothyroidism, myxedema. Myxedema produces a cutaneous and dermal odema caused by excess deposition of glycosaminoglycans, hyalauronic acid and some mucopolyssacharides in subcutaneous tissues (Mansourian 2010). CTS was commonly attributed to deposition of pseudo mucinous substances on the median nerve sheath (Golding 1970). This process is described similarly to that of myxedema.
It may be that this deposition alters the contractile properties of muscles leading to the delayed ankle jerk reflex. The deposition on the median nerves would reduce carpal tunnel space and when more severe could lead to lesions capable of effecting the conductivity of the nerve. However, initially it’s feasible it would not significantly alter the conductivity of the nerve but in functional tasks and mechanical tests the nerve has insufficient space in the carpal tunnel and signs are present. Therefore explaining results of Palumbo et al (2000).
Clinically it’s important to consider the effects of untreated hypothyroidism in patients with neural and musculoskeletal symptoms. This should form part of the thought process for patients with diagnosed and undiagnosed hypothyroidism. Clinicians should familiarise themselves with common symptoms of hypothyroidism to help them screen for potential hypothyroidism contributing to musculoskeletal symptoms.
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Golding, D.N., 1970. Hypothyroidism presenting with musculoskeletal symptomsAnn. rheum. Disease, 29, 10.
Lambert, E.H., Underdahl, L.O., Beckett, S. and Mederos, L.0., 1951. A study of the ankle jerk in myxedema. Journal clinical endocrinology, 11, 1186.
Mansourian, A.R., 2010. A review on post puberty hypothyroidism: A glance at myxedema. Pakistan journal of biological sciences, 13 (8), 866-878.
Olney, R.K., 2001. Carpal tunnel syndrome. Neurology, 56 (11), 1431-1432.
Palumbo, C.F., Szabo, R.M. and Olmsted, S.L., 2000. The effects of hypothyroidism and thyroid replacement on the development of carpal tunnel syndromeJournal of Hand Surgery, 25 (4), 734-739.
Schwartz, M.S. Mackworth-Young, C.G. and McKeran, R.O., 1983. The tarsal tunnel syndrome in hypothyroidism. Journal of Neurology, Neurosurgery, and Psychiatry, 46, 440-442
Solomon, D.H., Katz, J.N., Bohn, R., Mogun, H. and Avorn, J., 1999. Nonoccupational Risk Factors for Carpal Tunnel Syndrome. Journal of General Internal Medicine, 14 (5), 310–314.