Hypothyroidism
Adrenocorticotropin
Adrenocorticotropin Deficiency
Thyroid hormone, TSH levels were evaluated before and after adrenal replacement in 8 patients between 35 and 62 years of age with isolated ACTH (adrenocorticotropin) deficiency. In 3 of the 8 cases there appeared to be chronic thyroiditis. the prevalence of chronic thyroiditis coexisting in isolated ACTH deficiency may be higher than previously thought.
TSH excess before adrenal replacement may be attributed not only to direct enhancement of TSH release due to chronic cortisol deficiency, but also to thyroid dysfunction due to chronic thyroiditis. The authors state that it is possible that hypothyroidism due to chronic thyroiditis can be improved only by adrenal supplementation.
"Evaluation of Thyroid Function on Patients With Isolated Adrenocorticotropin Deficiency", Shigemasa, C et al, The American Journal of Medical Sciences, November 1992;304(5):279-284.
Lipoproteins & Hypothyroidism
Hyperlipoproteinemia
The incidence of hyperlipoproteinemia was 22.5% in this group of mild, subclinical hypothyroid patients, similar to those in the normal population of 21.5%. Approximately half of the patients with subclinical hypothyroidism, when supplemented with L- thyroxine, had a normalization total and LDL cholesterol.
the majority of patients with mild, subclinical hypothyroidism have normal lipid profiles, and treatment with L-thyroxine should be limited to those with elevated total and LDL levels. Treatment of all patients with subclinical hypothyroidism with L-thyroxine is not warranted.
"Subclinical Hypothyroidism and Hyperlipoproteinemia: Indiscriminate L-Thyroxine Treatment Not Justified", Bogner, U., et al, ACTA Endocrinologica, 1993;128:202-6.
Overtreating Hypothyroidism
Inadvertent excess thyroid hormone in the treatment of hypothyroidism can result in subclinical hyperthyroidism. It has been estimated that even in thyroid disease clinics, excessive dosages may occur in about 20% of the patients.
Symptoms of subclinical hypothyroidism tend to be very mild. Subclinical hypothyroidism effects more men than women. The cardiovascular system does not tolerate subclinical hyperthyroidism well. There is evidence for increased heart rate and contractility associated with subclinical hyperthyroidism. This can be a considerable problem. Atrial fibrillation is a symptom of subclinical hyperthyroidism along with arrhythmias and premature atrial beats. There is a problem with skeletal bone loss risk in patients with subclinical hyperthyroidism. In thyrotoxic patients, calcium metabolism is affected, accelerating bone remodeling.
It appears that thyroxine affects bone mass more in postmenopausal women than in premenopausal women. More bone is lost in cortical than trabecular bone and from the lumbar spine than the hip. It is noted the bone loss was not confirmed in all studies. No increase in fracture rate was found.
Physicians should be aware of the dosage of thyroid hormone in postmenopausal women who are smokers, since they have the greatest increased risk to osteoporosis.
"Overtreating Hypothyroidism is an Easy, Insidious Mistake", Cooper, Catherine, Family Practice News, June 1, 1993;5.
RA & Hypothyroidism
Rheumatoid Arthritis
In this study, thyroid dysfunction is seen at least 3 times more often in women with rheumatoid arthritis than in women with similar demographic features with non-inflammatory rheumatoid diseases such as osteoarthritis and fibromyalgia.
"Thyroid Dysfunction and Rheumatoid Arthritis: A Controlled Prospective Survey", Shiroky, J B et al, Annals of Rheumatic Diseases, 1993;52:454-456.
Subclinical Hypothyroidism
Subclinical hypothyroidism is defined as an elevated thyrotropin (TSH) level and a normal T4 or free T4 concentration in the absence of overt symptoms. The TSH level is elevated as a result of a decrease in feedback inhibition on the pituitary gland. Physiologic causes of elevated TSH levels include severe nonthyroidal disease, primary adrenal insufficiency and peripheral resistance to thyroid hormone. Chronic lymphocytic thyroiditis is a frequent cause. Treatment with either radioactive iodine or surgery is a common cause of subclinical hypothyroidism.
Iodine deficiency remains the most common cause worldwide of both subclinical and frank hypothyroidism. The prevalence of subclinical hypothyroidism is between 2.5% and 10.4%. The prevalence of subclinical hypothyroidism is much greater than that of overt hypothyroidism.
A general principal is to give the lowest dose necessary to normalize TSH levels. The principal risk of giving the medicine is suppressing TSH levels. Cardiac arrhythmias, atrial fibrillation and angina can also be aggravated. Some reports have suggested bone loss in overzealous females taking thyroid supplementation.
"Subclinical Hypothyroidism: Understanding is the Key to Decision Making", Cushing, Gary W., M.D., Postgraduate Medicine, July 1993;94(1):95-107.
Thyroxine & Hypothyroidism
Simultaneous ingestion of ferrous sulfate and thyroxine causes a reduction in thyroxine efficacy that becomes clinically significant in some patients. This reduction in thyroxine activity is probably due to the binding of iron to thyroxine. It is noted that many people require both thyroxine and iron supplementation. These 2 drugs should be separated by more than 2 hours between ingestion.
"Ferrous Sulfate Reduces Thyroxine Efficacy in Patients With Hypothyroidism", Campbell, N. Annals of Internal Medicine, December 15, 1992;117(12):1010-1013.
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