| The sick euthyroid syndrome can be described as | | | | other factors should be considered and this theory |
| abnormal findings on thyroid function tests in a patient | | | | does not account for the low levels of thyroxine as |
| with no known thyroid condition or nonthyroidal illness | | | | well. |
| (NTI). After recovering from the illness, the | | | | Another explanation suggests that the serum thyroid |
| abnormalities are reversible. However, most of these | | | | hormone abnormalities may be due to inhibition of |
| patients are admitted into the Intensive Care Unit so it | | | | hormone-binding proteins, which consequently prevents |
| is of utmost important that the syndrome be | | | | test from reflecting normal free hormone levels. This |
| differentiated from a real thyroid disorder. | | | | binding inhibitor can be found in both serum and tissues |
| There are many forms of the syndrome but one such | | | | and could inhibit binding to nuclear triiodothyronine |
| form is most common. In this form, there are low or | | | | receptors or prevent uptake of the thyroid hormones |
| lower than normal levels of total thyroxine and | | | | by the cells of the body. However, some studies have |
| triiodothyronine. In cases of true hypothyroidism, the | | | | failed to exhibit such a binding inhibitor. |
| low levels of thyroid hormones would send a | | | | Cytokines, too, have been thought to play a role in this |
| feedback signal to the pituitary gland to increase | | | | particular syndrome. These cytokines in particular are |
| secretion of thyrotropin or thyroid-stimulating hormone | | | | interleukin-1 and interleukin-6, tumor necrosis |
| (TSH) but not so in this condition. In this form of the | | | | factor-alpha, and interferon-beta. They were thought |
| syndrome, TSH levels remain within the normal range. | | | | to exert an effect on the hypothalamus, pituitary gland, |
| Pathophysiology | | | | and other tissues, inhibiting the production of |
| One such explanation for the abnormal findings in the | | | | thyroid-releasing hormone, thyroid-stimulating hormone, |
| syndrome involve the distinction between type 1 | | | | triiodothyronine, thyroid-binding globulins, and |
| deiodinase and type 2 deiodinase enzymes. Type 1 | | | | thyroglobulin. They were also thought to decrease the |
| deiodinase is usually found in the periphery while type 2 | | | | activity of type 1 deiodinase and the binding capacity |
| deiodinase is found mainly in the pituitary gland. In this | | | | of triiodothyronine nuclear receptors. |
| particular condition, it is the activity of type 1 deiodinase | | | | Treatment |
| which is decreased, resulting in less conversion of | | | | Although patients with the sick euthyroid syndrome |
| thyroxine to triiodothyronine. | | | | may exhibit signs of hypothyroidism such as |
| Despite all this, the type 2 deiodinase is not as | | | | hypothermia and a sluggish sensorium, they are not |
| affected as the type 1 deiodinase and the pituitary | | | | hypothyroid and should not receive thyroid hormone |
| gland continues to sense normal levels of | | | | replacement as treatment. Treatment of such patients |
| triiodothyronine. Because of this, the pituitary gland will | | | | with thyroid hormone may, in fact, yield either no |
| inhibit the secretion of TSH due to what it perceives | | | | improvement or a worse outcome. |
| as normal concentrations of triiodothyronine. However, | | | | |