Complications of overreplacement with levothyroxine sodium Include the following:
- Accelerated bone loss
- Reduction in bone mineral density
- Osteoporosis
- Increased heart rate
- Increased cardiac wall thickness
- Increased contractility
The last three problems above increase the risk of cardiac arrhythmias (especially atrial fibrillation), particularly in the elderly population.
Medications that suppress TSH production include steroids, dopamine, dobutamine, and octreotide.
Up to 30-40% of patients with hypothyroidism have anemia, usually from decreased erythropoiesis. In 15% of patients, the anemia is of the iron deficiency type, with microcytosis and hypochromia. Although this can be a normocytic normochromic anemia, the most common morphologic abnormality is a macrocytic anemia that may be partially due to insufficient vitamin B-12 and folate intake.
Glomerular filtration rate, renal plasma flow, and renal free water clearance are all decreased in hypothyroidism and may result in hyponatremia.
Prolactin may be elevated in primary hypothyroidism. This is thought to be caused by overlap secretion due to stimulation of the lactotroph by the elevated TRH level. The decreased clearance of prolactin in hypothyroidism may also play a contributory role. The elevated prolactin level leads to decreased gonadotropin secretion and decreased responsiveness to GnRH. The result of this is anovulatory cycles with menstrual abnormalities, galactorrhea, and infertility in some patients.
Medications that suppress TSH production include steroids, dopamine, dobutamine, and octreotide.
Up to 30-40% of patients with hypothyroidism have anemia, usually from decreased erythropoiesis. In 15% of patients, the anemia is of the iron deficiency type, with microcytosis and hypochromia. Although this can be a normocytic normochromic anemia, the most common morphologic abnormality is a macrocytic anemia that may be partially due to insufficient vitamin B-12 and folate intake.
Glomerular filtration rate, renal plasma flow, and renal free water clearance are all decreased in hypothyroidism and may result in hyponatremia.
Prolactin may be elevated in primary hypothyroidism. This is thought to be caused by overlap secretion due to stimulation of the lactotroph by the elevated TRH level. The decreased clearance of prolactin in hypothyroidism may also play a contributory role. The elevated prolactin level leads to decreased gonadotropin secretion and decreased responsiveness to GnRH. The result of this is anovulatory cycles with menstrual abnormalities, galactorrhea, and infertility in some patients.
Other studies may be performed in the evaluation of complications of primary hypothyroidism (when indicated). These tests are usually not performed and are not necessary in routine diagnosis or evaluation of hypothyroid patients.
- Chest radiograph - May show small pleural effusions
- Electrocardiogram (ECG) - May show low-voltage QRS tracing, nonspecific ST-wave changes, and premature ventricular contractions; prolongation of the QT interval with torsade de pointes and ventricular tachycardia may be noted
- Echocardiogram - May show some pericardial effusion in severe cases of hypothyroidism
Long-Term Monitoring
Upon the initiation of the levothyroxine replacement therapy, check thyroid function tests, specifically TSH, initially every 6-8 weeks as dose adjustments are made. After the attainment of the clinical euthyroid state and a normal TSH level, patients and the TSH levels may be checked every 6-12 months.More frequent follow-up and TSH checks may need to be performed when patients start taking medications, such as ferrous sulphate, calcium supplementation, and multivitamins, that have the potential to impair the absorption of levothyroxine and therefore to affect the TSH level. Patients need to be advised to separate these medications from levothyroxine by at least 4 hours.Follow-up care should include clinical evaluation for symptoms of hypothyroidism or iatrogenic hyperthyroidism.Physical examination should routinely include weight measurement, pulse and blood pressure determinations, and thyroid examination for the presence of nodules.Yearly thyroid ultrasonographic evaluation is important in patients with Hashimoto thyroiditis because of the increased risk of thyroid nodules in these patients and for follow-up of patients with existing benign thyroid nodules.
