It is well documented that musculoskeletal conditions, such as carpal tunnel syndrome, Dupuytren’s contracture and trigger finger, occur in association with thyroid disease. Most disorders occur with hypothyroidism, but there have been occurrences with thyrotoxicosis as well. Although there is limited research to support a clear association between hypothyroidism and plantar fasciitis, it is theorized that low thyroid levels will increase the susceptibility for the development of plantar fasciitis.
Plantar fasciitis is the tearing, inflammation and deterioration of the plantar fascia, a connective tissue band which supports the arch. Plantar fasciitis classically causes heel pain at the first step in the morning or upon rising after long periods of rest. The plantar fascia is similar in structure to a ligament and is composed of mostly collagen, but also elastin and GAGs, which are long carbohydrate chains known to attract water and increase resiliency. Musculoskeletal disorders result from hypothyroidism because low thyroid levels cause deposits within the connective tissue. This occurs because thyroid hormone inhibits fibroblasts. Fibroblasts are cells within connective tissue which produce and secrete substances important in connective tissue structure, such as collagen, elastin, GAGs and fibronectin. With normal levels of thyroid hormone, these substances are not overproduced. When thyroid levels are low, fibroblasts overproduce these substances, particularly GAGs. GAGs attract water and increased deposits in the fascia disrupt the collagen network by increasing the space between collagen fibers. The strength of the plantar fascia is due in part to the organized array of collagen fibers. The additional GAGs, additional water content and increased spacing decreases the overall strength of the fascial band, which increases it’s susceptibility to tearing. Microscopic tears may occur in the plantar fascia under normal conditions, and this results in plantar fasciitis.
Clin Endocrinol (Oxf). 2003 Aug;59(2):162-7.
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