Diseases of the thyroid gland are common and cause either a flaw in the size or shape of the gland which becomes known as "goiter".  Goiter may also be the result of a flaw in the secretions of the gland's hormones. 
Clinical symptoms of hyperthyroidism (Thyrotoxicosis)
Increase in the secretions of   the thyroid gland affects one or more body organ. The most important symptom of malfunction of the thyroid gland is excessive nervousness, increased perspiration, inability to withstand hot weather, increased palpitations, panting, rapid fatigue, weight loss, hand tremble, reduced sleeping hours and ocular symptoms affecting vision.  Of the important illnesses are:  Enlarged appetite, increased defecation as well as irregular menstruation in females. 
Clinical examination can reveal:  Increase in size of the thyroid gland, bulging of the eyes and recession of the upper eyelids. Often these signs are not apparent in elderly patients and only irregular heartbeats and general weakness are obvious. It has been found that in all diseases of the thyroid gland, the symptoms of hyperthyroidism are more apparent in women than in men. 
Clinical symptoms of hypothyroidism
This takes place when the effect of the hormone over body tissue and organs decreases.  This occurs mostly as a result of decreased hormone secretion by the gland.  In certain rare cases this is caused by the none responsiveness of the tissue to the hormone present in normal or excessive amounts in the blood which explains the reason for resistance to the hormone's function.
Hypothyroidism is indicated by swelling of the body tissue called "Myxedema"
Symptoms of hypothyroidism are usually unnoticed and may develop and increase with time.  In classic cases these include:
    Inability to tolerate low weather temperatures (preference for warm weather, thick clothes, use of heavy covering during sleep in hot weather)
    Muscle cramps and pain
    Hoarse voice, diminished hearing, rough skin, weight gain in spite of stable appetite, chronic constipation  and laziness.
    Cold skin, skin discoloration - mostly pale, swelling of the eyelids as well as hands and feet, as well as slowness in motion, thought and assimilation.
    More symptoms may affect blood circulation, the heart - reduced number of heartbeats, circulatory failure and cardial effusion as well as high blood pressure. in severe cases this may end in Coma.
    In newborn infants, the reduction of thyroid gland hormone secretion is always accompanied by mental retardation and certain manifest changes in the physical appearance of the infant.
    Reduced secretions of the thyroid gland in children or youth also lead to short stature
Laboratory diagnosis of Thyroid Gland malfunctions:
Tests to diagnose malfunction of the Thyroid gland:
    Free T3 & Free T4 to assess to amount of hormone available for the tissue
    TSH using the latest technology to  prove cases if increased or decreased hormone.  The importance of this test is clearly manifest  in case of hypothyroidism
Important Tests to Identify the Causes of Malfunction of the Thyroid gland 
    Autoantibodies resulting from autoimmune disease
    Thyroglobulin to assess the development of cancer of the  thyroid gland
    in cancer patients and their response to treatment.
    Biopsy of the thyroid gland to examine the cells for malignancy.