The thyroid gland produces the hormones thyroxine, or T4, and triiodothyronine, or T3. The thyroid hormone levels in the circulation determine the activity rate of the body tissues, also known as the metabolic rate. Hyperthyroidism describes the condition of abnormally elevated thyroid hormone levels, which causes an increased metabolic rate. Hypothyroidism causes an abnormally decreased metabolic rate due to low thyroid hormone levels. Signs of thyroid problems typically prompt blood testing to measure circulating concentrations of T3 and T4.
Goiter
Hyperthyroidism or hypothyroidism can cause thyroid enlargement, commonly known as a goiter. The most frequent cause of these disorders is an autoimmune attack on the thyroid, notes Merck Manuals Online Medical Library. Autoimmune hyperthyroidism is Graves' disease, and Hashimoto's thyroiditis is autoimmune hypothyroidism. Either disorder may cause a goiter, especially in the early stages of the illness.
Weight Change
The metabolic rate influences the number of calories needed to maintain basic bodily functions. The increased metabolic rate of hyperthyroidism often causes unintentional weight loss, as the body burns an increased number of calories. Weight loss frequently occurs despite a normal or exaggerated appetite, notes the University of Maryland Medical Center. In contrast, reduction in the metabolic rate frequently causes weight gain in people with hypothyroidism.
Abnormal Body Temperature
Cellular metabolism generates body heat. The elevated metabolic rate of hyperthyroidism may cause moderately increased body temperature, with an associated feeling of overheating. Hypothyroidism often causes decreased body temperature, according to the Merck Manuals Online Medical Library. People with hypothyroidism frequently express discomfort in cool environmental temperatures.
Skin Disturbances
The low level of overheating associated with hyperthyroidism often causes skin flushing and moistness due to increased sweating. Conversely, hypothyroidism often causes skin paleness, accompanied by dryness and a coarse texture. Yellowing of the skin may occur on the palms and soles.
Hair Loss
Hair loss can occur with hyperthyroidism or hypothyroidism, although this symptom is more characteristic of low thyroid hormone activity. With hypothyroidism, the hair takes on a coarse texture and often becomes brittle, notes Dr. James Norman on Endocrineweb.com. Nail brittleness may also occur in people with an underactive thyroid.
Facial Changes
Increased circulating thyroid hormones may cause eye changes termed exophthalmos, characterized by eye bulging and a wide-eyed, staring gaze. People with hypothyroidism may demonstrate a dull facial expression and drooping eyelids. Facial puffiness may occur, especially around the eyes, reports Merck Manuals Online Medical Library. Some people with longstanding hypothyroidism have tongue enlargement due to protein accumulation in the tongue tissues.
Heart Rate Changes
Hyperthyroidism causes a predictable increase in heart rate, which may be accompanied by rhythm irregularities. Patients commonly describe heart palpitations due to the rapidity and force of the heart contractions. In contrast, people with hypothyroidism often demonstrate an unusually low heart rate.
References
- Merck Manuals Online Medical Library: Hyperthyroidism, Signs and Symptoms
- Merck Manuals Online Medical Library: Hypothyroidism, Signs and Symptoms
- University of Maryland Medical Center: Hypothyroidism, Symptoms
- University of Maryland Medical Center: Hyperthyroidism
- American Association of Clinical Endocrinologists: Medical Guidelines for Clinical Practice for the Evaluation and Treatment of Hyperthyroidism And Hypothyroidism
