Subclinical hypothyroidism: neurobehavioral features and beneficial effect of l-thyroxine treatment

Abstract

Frank hypothyroidism is known to induce neurological and mental dysfunction. The aim of this study was to assess selected neuropsychological and behavioral features by means of standardized tests in a group of 14 patients with subclinical hypothyroidism who were free from neuropsychological complaints and to evaluate the possible effects of L-thyroxine treatment on their performance. Patients were submitted to the Crown and Crisp Experiential Index and to the Wechsler Memory Scale; their ratings on the neurobehavioral tests and their thyroid hormone profile were compared to those of a control group of 50 age-and sex-matched subjects. Comparison was also carried out between pretreatment ratings and those obtained following a 6-month L-thyroxine course (0.1-0.15 mg/day). The Wechsler Memory Scale ratings showed a significant impairment in patients' memory-related abilities [memory quotient (MQ) = 89.1 _+ 2.9; P = 0.002 (patients versus controls)] ; the Crown and Crisp Experiential Index ratings demonstrated moderate differences between untreated patients and controls with respect to hysteria (P=0.03), anxiety (P=0.05), somatic complaints (P = 0.0005), and depressive features (P= 0.002) scales; the total score was also significantly higher (42.0 + 3.8 ; P = 0.005). After L-thyroxine treatment the patients' performances showed an improvement in memory skills, as evaluated by the Wechsler Memory Scale [MQ= 99.9 + 4.0; P= 0.002 (treated versus untreated)] ; somatic complaints (P=0.02) and obsessionality (P = 0.04) ratings and the Crown and Crisp Experiential Index total score (P = 0.04) significantly decreased with respect to untreated patients. The remarkable effects of L-thyroxine treatment observed in the present study indicate that patients with subAbbreviations: TSH=thyrotropin; TRH=thyrotropin-releasing hormone; L-T4=levothyroxine; TT4=total thyroxine; FT 4=free thyroxine, TTa =total 3,5,3'-triiodothyronine; FT3=free 3,5,3'-triiodothyronine, WMS=Wechsler Memory Scale; CCEI = Crown and Crisp Experiential Index clinical hypothyroidism may require early therapy to provide specific treatment for their neuropsychological alterations and to avoid progression toward frank hypothyroidism.Frank hypothyroidism has long been known to induce major neurological and psychological dysfunction [14] ; in particular, depression, mania, and dementia or dementialike features may occur. Moreover, it has been reported to occur more commonly in lithium-treated patients suffering from bipolar affective illness than in unselected psychiatric patients [22] ; a high prevalence of hypothyroidism has also been reported in a subgroup with the "rapid cycling" form [4,6]. Several studies also suggest that subclinical hypothyroidism, an apparently asymptomatic state with normal serum thyroid hormone and increased thyrotropin (TSH) concentrations [10], may be associated with some psychiatric disorders, such as bipolar affective illness [6,16,17]. There is growing evidence for the presence of metabolic and cardiovascular abnormalities rather simil...

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