Presumptive nonthyroidal illness syndrome in critically ill foals

Hypothalamic-pituitary-thyroid (HPT) axis dysfunction is associated with morbidity and mortality in critically ill people. To date, investigations of HPT axis in critically ill foals are limited.

To document the occurrence of low thyroid hormone concentrations (presumptive nonthyroidal illness syndrome; NTIS) in critically ill newborn foals and investigate whether NTIS is associated with severity of disease and outcome.

NTIS occurs frequently in foals with sepsis and is associated with sepsis score and outcome. Reverse T3 (rT3) concentrations will be increased in septic foals and highest in nonsurvivors.

Thyroid hormones (total and free thyroxine [TT4 and fT4], total and free tri-iodothyronine [TT3 and fT3], reverse T3 [rT3]) were prospectively measured in healthy, sick nonseptic and septic foals. Clinical and laboratory information was retrieved from the medical records. Hormones were measured by validated radioimmunoassays.

Concentrations of all thyroid hormones except rT3 (P = 0.69) were decreased in septic and sick nonseptic foals (P < 0.01). Reductions in hormone concentrations were associated with an increased sepsis score (P < 0.01). Nonsurviving septic foals had lower TT4, fT4, TT3 and fT3 concentrations than surviving septic foals (P < 0.01). rT3 concentrations were higher in nonsurviving septic prematurefoals than surviving septic premature foals (P < 0.05).

NTIS (euthyroid sick syndrome) is frequently observed in critically ill and premature foals, and associated with severity of disease and mortality.

More research is needed to better understand the mechanism of this finding and determine whether manipulation of the HPT axis or thyroid replacement therapy could be beneficial.