Severe hypothyroidism (SH) is a rare but life-threatening endocrine emergency. Only a few data are available on its management and outcomes of the most severe forms requiring ICU admission. We aimed to describe the clinical manifestations, management, and in-ICU and 6-month survival rates of these patients.

We conducted a retrospective, multicenter study over 18 years in 32 French ICUs. The local medical records of patients from each participating ICU were screened using the International Classification of Disease 10th revision. Inclusion criteria were the presence of biological hypothyroidism associated with at least one cardinal sign among alteration of consciousness, hypothermia and circulatory failure, and at least one SH-related organ failure.

Eighty-two patients were included in the study. Thyroiditis and thyroidectomy represented the main SH etiologies (29% and 19%, respectively), while hypothyroidism was unknown in 44 patients (54%) before ICU admission. The most frequent SH triggers were levothyroxine discontinuation (28%), sepsis (15%), and amiodarone-related hypothyroidism (11%). Clinical presentations included hypothermia (66%), hemodynamic failure (57%), and coma (52%). In-ICU and 6-month mortality rates were 26% and 39%, respectively. Multivariable analyses retained age > 70 years [odds ratio OR 6.01 (1.75–24.1)] Sequential Organ-Failure Assessment score cardiovascular component ≥ 2 [OR 11.1 (2.47–84.2)] and ventilation component ≥ 2 [OR 4.52 (1.27–18.6)] as being independently associated with in-ICU mortality.

SH is a rare life-threatening emergency with various clinical presentations. Hemodynamic and respiratory failures are strongly associated with worse outcomes. The very high mortality prompts early diagnosis and rapid levothyroxine administration with close cardiac and hemodynamic monitoring.