Thyrotoxicosis subclinical

Subclinical or mild thyrotoxicosis is defined as a low TSH with a normal FT4 level. While there may be few or no symptoms in these patients, there are several areas of concern.31,32 Many patients will progress to overt thyrotoxicosis. Patients with subclinical hyperthyroidism have been shown to suffer long-term cardiovascular and bone sequelae. In a 10-year follow-up of 2007 patients over age 60,33 patients with an undetectable TSH level had a 3.1-fold increased risk of atrial fibrillation versus those with a normal TSH. In a different 10-year follow-up study34 of... 

Patients with beta-thalassemia major have an increased risk of primary hypothyroidism. In 23 patients with beta-thalassemia amiodarone was associated with a high risk of overt hypothyroidism (33 versus 3% in controls) (43). This occurred at up to 3 months after starting amiodarone. The risk of subclinical hypothyroidism was similar in the two groups. In one case overt hypothyroidism resolved spontaneously after withdrawal, but the other patients were given thyroxine. After 21-47 months of treatment three patients developed thyrotoxicosis, with remission after withdrawal. There were no cases of hyperthyroidism in the controls. The authors proposed that patients with beta-thalassemia may be more susceptible to iodine-induced hypothyroidism, related to an underlying defect in iodine in the thyroid, perhaps associated with an effect of iron overload. 

The addition of liothyronine 25 micrograms daily was found to increase the speed and efficacy of imipramine in relieving depression. Similar results have been described in other studies with desipramine or amitriptyline but the reasons are not understood. One possible explanation is that the patients had overt or subclinical hypothyroidism, which after correction with liothyronine allowed them to overcome an impaired response to tricyclic antidepressants." However, adverse reactions have also been seen. A patient being treated for both hypothyroidism and depression with thyroid 60 mg and imipramine 150 mg daily complained of dizziness and nausea. She was found to have developed paroxysmal atrial tachycardia. A 10-year-old girl with congenital hypothyroidism, well controlled on desiccated thyroid 150 mg daily, developed severe thyrotoxicosis after taking imipramine 25 mg daily for 5 months for enuresis. The problem disappeared when the imipramine was withdrawn. In another patient the effect of levothyroxine was lost and hypothyroidism developed when dosulepin was started. ... 

Thyroid hormones are typically produced in struma ovarii and struma carcinoids of the ovary in subclinical levels. Hyperthyreosis seems to be present in only 25%, and thyrotoxicosis occurs in only 5% of patients with struma ovarii (Fig. 9.13) [37]. Primary... 

Eustatia-Rutten CF, Corssmit EP, Heemstra KA, Smit JW, Schoemaker RC, Romijn JA, Burggraaf J. Autonomic nervous system function in chronic exogenous subclinical thyrotoxicosis and the effect of restoring euthyroidism. J Clin Endocrinol Metab 2008 93(7) 2835 1. 

Severe multisystem trauma, endotoxemia, or situations in which there is a raised metabolic demand for thiamin, such as pregnancy, thyrotoxicosis, and intercurrent illness or impaired absorption (e.g., alcohol abuse or gastrointestinal disease or resection), can produce subclinical evidence of thiamin deficiency or more severe life-threatening aspects of beriberi, such as renal and/or cardiovascular failure. The elderly may be particularly at risk of subclinical thiamin deficiency. One Belgian study on patients with a mean age of 83 years reported that 40% had a raised TDP effect (>15%), in whom there was a high proportion of Alzheimer s disease, depression, cardiac failure, and falls. The diuretic furosemide was also more frequently taken by the thiamin-deficient patients. 

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