Thyroid stimulating hormone, usually abbreviated TSH, is manufactured by the pituitary gland. Release of TSH stimulates the thyroid to make T3 and T4, the hormones responsible for thyroid function. If the thyroid stops functioning, TSH levels rise as the body attempts to "force" the thyroid to produce hormones. This reaction, known as a feedback loop, causes TSH levels to rise above their normal range. High blood levels of TSH indicate an underactive thyroid, or hypothyroid, a condition that affects as many as 10 percent of women and six percent of men older than age 65 years, the Merck Manual states, and causes a variety of symptoms.
High TSH levels due to underactive thyroid causes many changes in the skin and hair. Skin often becomes dry, scaly, thick and pale. Palms and soles of the feel may appear yellowish due to the deposit of carotene. Hair thins and turns dry and coarse. Fluid retention and weight gain may occur, along with puffiness of the face and swelling around the eyes. The facial expression may appear dull; eyelids may droop. Nails become brittle and break easily. The tongue may be enlarged.
People with elevated TSH often experience mental changes. They may become depressed, suffer memory loss, and have difficulty processing information. Speech may be slow and dementia may occur. If TSH hormone levels are extremely low for long periods of time a life-threatening condition called myxedema coma may occur.
High TSH levels from thyroid disease lead to muscle and joint aches and pains, along with stiffness and swelling. Weakness and loss of deep tendon reflexes may occur. Numbness and tingling in the extremities commonly occur.
Systemic symptoms of high TSH from underactive thyroid include cold sensitivity due to a low body temperature, sluggishness and fatigue. If myxedema coma develops, seizures and coma can occur.
Elevated TSH levels from low-functioning thyroid can cause cholesterol levels to rise. Heart enlargement and heart failure can occur even in people with subclinical thyroid disease, which has few symptoms, the Mayo Clinic warns. Fluid can build up around the heart and lungs and the heart rate may become bradycardic, or slower than normal.
Women with high TSH levels may have heavier than normal periods or no periods at all. Infertility can occur due to a lack of ovulation. Sex drive often decreases.