Prevalence and pattern of sick euthyroid syndrome in acute and chronic non-thyroidal illness--its relationship with severity and outcome of the disorder.

BACKGROUND: Non-thyroidal illness is a common cause of alterations in thyroid hormone economy in absence of underlying intrinsic thyroid disorder.
OBJECTIVE: To study the prevalence and pattern of alterations in thyroid hormone economy in various non-thyroidal illnesses in our region and also to correlate these alterations with the severity and outcome of the non-thyroidal illness.
MATERIAL AND METHODS: We analyzed circulating T3, T4, TSH in 382 patients with non-thyroidal illness (285 acute and 97 acute on chronic) and correlated the alterations with severity and outcome of the non-thyroidal disorder. The patients had one or more organ failure at the time of enrollment to the study. The hormones were estimated at the onset of sickness, and at 3rd and 24th week. T3, T4 and TSH in 75 age and sex matched euthyroid subjects were taken as controls.
RESULTS: T3 (mean +/- SEM) was significantly reduced at the onset of illness, in both acute and chronic patient groups (1.61 +/- 0.05 nmol/l) compared to that in the controls (3.17 +/- 0.06 nmol/l). In spite of clinical improvement in most instances, T3 continued to remain low in the 3rd week (1.49 +/- 0.11 nmol/ l) but increased (2.14 +/- 0.09 nmol/l) in 24th week. Low T3 was found in 93 (32.6%) cases with acute illness in 20 (20.6%) cases with chronic illness. A combination of low T3 and T4 was found in 35 (12.3%) of cases with acute and 15 (15.5%) with chronic illness. Although serum TSH showed noticeable fall and rise in some individuals, no significant difference in mean TSH was observed during any period of illness compared to that in the controls. Severity of illness correlated with decrease in T3 (r=0.58) and T4 (r=0.38). A low T3 and T4 with low or undetectable TSH were associated with increased mortality. At the onset of acute illness low T3 was seen in 113 (29.6%, low T3 -low T4 in 50 (13.1%), high T4 in 28 (7.3%) lowT3-lowT4- low TSH in 10 (2.6%) and low T4 alone in 4 (1%) patients. Fifty one 1 (13.4%) of our patients demonstrated alterations in TSH in presence of normal T3 and T4-26 patients had decreased TSH while as 25 had increased TSH. Of 118 patients who followed at 24 weeks, 11 (9.3%) had low T3, 7(5.9%) had low T3- low T4 and 13 (11%) had elevated TSH.
CONCLUSION: Pattern and prevalence of sick euthyroid syndrome in this part of the world, a recognized iodine deficient region, appears to be similar to that reported elsewhere. Important finding in our study was higher percentage of TSH elevation, which we believe to reflect the underlying iodine deficiency state of our community. Besides a significant number of subjects persisted with alterations in thyroid functions even after 6 months of therapy. Though the severity of thyroid hormone derangement correlated with severity of sickness, the derangement was similar in acute vs. acute on chronic nonthyroidal illnesses.