Plantar fasciitis and thyroid dysfunction
Plantar fasciitis is characterized by sharp pain in the heel that occurs on the first step in the morning or upon waking up after periods of rest. Fasciitis is caused by microscopic tears in the plantar fascia, a long structure of connective tissue on the sole of the foot. Tearing of the fascial band causes inflammation and eventual deterioration. The plantar fascia is composed mainly of collagen, but also elastin and long chains of carbohydrates called glycosaminoglycans or GAGs. The organized network of collagen adds to its strength, elastin allows stretching and GAGs attract water, improving resilience.
Musculoskeletal disorders are often associated with thyroid disease, particularly hypothyroidism. Common musculoskeletal complaints in hypothyroid patients are muscle tenderness, generalized joint pain, cramps, and weakness. Specific musculoskeletal disorders, such as adhesive capsulitis and carpal tunnel syndrome, have been linked to hypothyroidism. It is theorized that hypothyroidism can cause plantar fasciitis for the same reason that other musculoskeletal conditions occur in hypothyroid patients. The disorders are the result of low thyroid levels causing deposits within the connective tissue. Thyroid hormone inhibits the production of fibroblasts and the secretion of collagen, elastin, and GAG, all important substances in the structure of connective tissue. Low thyroid hormone levels result in the overproduction of these substances, particularly GAGs, which attract water.
The increased GAG deposits and the additional water increase the space between the collagen fibers. This disrupts the collagen network and compromises the integrity of the plantar fascia structure. The weakening of the plantar fascia increases its susceptibility to microscopic tears. Microscopic tear occurs when the plantar fascia is put under excessive stress. This commonly occurs with biomechanical conditions, but in a weakened plantar fascia, it can occur under normal conditions. Lacrimation causes inflammation and pain. Due to the early disruption of the collagen network, the progression from plantar fasciitis, an inflammatory condition resulting from the tear, to plantar fasciosis, a degenerative condition, can occur more rapidly. Plantar fasciosis is a more difficult condition to treat, making early diagnosis and treatment crucial.
Eliminating tension in the plantar fascia is an important early treatment. This can be accomplished by wearing supportive shoes and insoles and avoiding walking barefoot. Heel lifts, or shoes with a small heel, will also eliminate arch tension. Heel cups can help relieve symptoms, but they will not lessen the stress on the plantar fascia or improve the condition. Losing weight will decrease stress on the arch, unfortunately weight gain is common in hypothyroid patients and weight loss tends to be difficult. Stretching both the calf and the arch are important in the healing process and specific stretching regimens should be started immediately after diagnosis. A night splint can facilitate healing and eliminate morning heel pain by stretching the plantar fascia overnight.