There may not be enough thyroid tissue to supply adequate thyroid hormoneAfter a subtotal thyroidectomy the thyroxine output may be inadequate to maintain an appropriate metabolic rate. Hypothyroidism is a decrease in thyroid functioning, not a slowing of the entire body's functions. In hypothyroidism the level of TSH from the pituitary usually is increased. Atrophy of the remaining thyroid tissue does not occur.