Association between Thyroid-Stimulating Hormone Level and Bell's Palsy

Objective To investigate whether dysregulated thyroid hormone function is associated with Bell's palsy. Study Design Cross-sectional. Setting Electronic medical record database of Clalit Health Services (CHS). CHS is an Israeli payer-provider, integrated health care system, serving >4.5 million members (54% of the Israeli population). Patients Older than 18 years with Bell's palsy, during 2002 to 2019. Interventions None. Methods A total of 1,374 patients with Bell's palsy who had thyroid-stimulating hormone (TSH) blood levels measured up to 60 days before the palsy were matched (1:2) for age and sex with 2,748 controls who had TSH blood levels and no history of Bell's palsy. Results Retrospective review of the CHS database, from 2002 to 2019 yielded 11,268 patients with Bell's palsy, of which, 1,374 met the inclusion criteria. Mean age was 57.9 years, and 61.4% were female. A higher percentage of patients in the Bell's palsy group had low TSH (≤0.55 mIU/L) compared with controls (5.7% vs. 3.6%, p < 0.001). Low TSH compared with TSH > 0.55 mIU/L, was independently associated with 1.45-fold increased odds for having Bell's palsy (95% CI 1.11-2.02, p < 0.001), when controlled for age, sex, body mass index, diabetes, hypertension, prior cerebrovascular accident, hemoglobin level, and purchasing thyroid hormone drugs. Among the patients with TSH ≤ 0.55 mIU/L, 95.5% had normal free thyroxin and 97.7% had normal free triiodothyronine levels (subclinical hyperthyroidism). For 47.1% of patients, TSH remained ≤0.55 mIU/L, 3 to 12 months after the Bell's palsy occurred and most patients had normal free thyroxin (95.4%) and normal free triiodothyronine (91.8%). Conclusions Subclinical hyperthyroidism is independently associated with Bell's palsy after controlling for multiple confounding factors.