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

Summary 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 subclinical hypothyroidism may require early therapy to provide specific treatment for their neuropsychological alterations and to avoid progression toward frank hypothyroidism.Abbreviations TSH thyrotropin - TRH thyrotropin-releasing hormone - l-T₄ levothyroxine - TT₄ total thyroxine - FT₄ free thyroxine - TT₃ total 3,5,3-triiodothyronine - FT₃ free 3,5,3-triiodothyronine - WMS Wechsler Memory Scale - CCEI Crown and Crisp Experiential Index