Low thyroid-stimulating hormone, or TSH, levels can lead to symptoms such as fatigue, leg cramps, dry skin and a feeling of being too cold and can cause an underactive thyroid gland, or hypothyroidism, explains Cleveland Clinic. Symptoms of low TSH levels caused by an overactive thyroid, or hyperthyroidism, include nervousness, rapid heart rate, weight loss, irregular menstruation and a feeling of being hot, explains WebMD. Damage to the thyroid gland, which creates TSH, causes these low levels, Cleveland Clinic states.
Hyperthyroidism can be caused by a form of goiter, a noncancerous tumor called a toxic nodule or Graves' disease, a type of autoimmune disorder, states WebMD. Doctors often test TSH levels to help diagnose underlying thyroid problems or to help manage thyroid treatment options. Low TSH levels, for example, can be caused by a patient taking too much medicine for an underactive thyroid.
TSH is part of a chain of hormones responsible for instructing the thyroid to make the hormones triiodothyronine and thyroxine, WebMD explains. These play a role in regulating the body's metabolism and maintaining normal brain growth, particularly in young children. When using TSH levels to help diagnose thyroid conditions, doctors often measure and consider triiodothyronine (called T3) and thyroxine (T4) levels as well.