Favorable Influence of Subclinical Hypothyroidism on the Functional Outcomes in Stroke Patients

Abstract

Abstract. Subclinical hypothyroidism (SCH) is thought to have an influence on stroke outcomes. However, few reports demonstrate a favorable relationship between the two. We evaluated this association in acute ischemic stroke. From Jan 2005 to Jun 2008, 756 acute ischemic stroke patients were recruited within seven days of onset. The patients with overt hypothyroidism/hyperthyroidism or other medical conditions that may affect thyroid function were excluded. Thyroid stimulating hormone (TSH) and free thyroxine (FT4) levels were measured within two days. Patients were divided into two groups: the SCH group (TSH > 5.0 μU/mL and normal FT4 levels) and the control group. Stroke outcomes were assessed using two different criteria. In the first outcome model, favorable outcomes [I] were simply defined by modified Rankin Scale (mRS) scores (≦ 1), while the favorable outcomes [II] were defined as follows: a) a mRS score of 0, if the baseline National Institute of Health Stroke Scale (NIHSS) scores were < 8, b) a mRS score of 0 or 1, if the NIHSS scores were 8-14, c) a mRS score 0-2, if the NIHSS scores were >14. The changes in mRS scores and the proportion of patients with favorable outcomes [I] p=0.003). We found that acute ischemic stroke patients with SCH at admission were more likely to show favorable functional outcomes than those without SCH. We can suggest preconditioning before the stroke combined with a reduced response to stress as a possible protective mechanism.

Associations between Thyroid Stimulating Hormone Levels and Both Severity and Early Outcome of Patients with Ischemic Stroke

“…Similarly, in another study, a greater proportion of patients in the subclinical hypothyroid group achieved a favorable outcome at 1 and 3 months [7] , whereas no significant difference in the proportion of patients with a good outcome at 1 year according to TSH levels was reported in the study by Alevizaki et al [8] . It is worth pointing out that no adjusted analyses were performed in these 2 studies, thus making it difficult to interpret the findings.…”

“…Two studies reported higher NIHSS scores at admission in IS patients with low triiodothyronine (T3) hormone levels [5,6] . Three other studies considered subclinical hypothyroidism based on TSH levels [7][8][9] . Among these studies, 2 studies found no significant difference in initial NIHSS scores [7,9] , although in one of these a trend toward a lower mean NIHSS score was noted in patients with subclinical hypothyroidism [9] .…”

“…Three other studies considered subclinical hypothyroidism based on TSH levels [7][8][9] . Among these studies, 2 studies found no significant difference in initial NIHSS scores [7,9] , although in one of these a trend toward a lower mean NIHSS score was noted in patients with subclinical hypothyroidism [9] . In the study by Alevizaki et al [8] , severity at admission was measured by the Scandinavian Stroke Scale, and the authors showed a greater frequency of mild neurological deficits in patients with high TSH levels.…”

“…Nonetheless, the dose- effect relationship we found suggests the existence of a plausible biological pathophysiological mechanism underlying the observed associations. Several hypotheses have been put forward including ischemic preconditioning induced by increased systemic vascular resistance, increased arterial stiffness, endothelial dysfunction [16,17] and chronic hypometabolism conferring a protective effect on brain tissue [7] , and reduced adrenergic stimulation inducing a lower response to physical stress in patients with subclinical hypothyroidism [18] . Several limitations must be acknowledged.…”

“…In addition, several studies assessed the influence of subclinical hypothyroidism on post-stroke outcome with conflicting conclusions [5][6][7][8][9] . Although low blood T3 concentrations appeared to be a predictive factor of a poorer prognosis after stroke in some studies [5,6] , subclinical hypothyroidism was shown to be associated with a better functional outcome in others [7][8][9] . Disparities are probably explained by various limitations, including a small sample size, a contro-versial definition of subclinical hypothyroidism or a lack of control for potential confounding factors in multivariable analyses.…”