Inherited condition resulting in clinical euthyroidism or hypothyroidism in the presence of elevated serum thyroxine concentrations. End-organ unresponsiveness to thyroid hormone. Other features include congenital deafness, goiter, and exophthalmos.
Thyroid Hormone Unresponsiveness; Thyroid Hormone Resistance.
Estimated between 1/40,000 and 1/50,000 live births.
Resistance to thyroid hormone is caused by mutation of the THRB gene on 3p24.2 and leads to a defect of the nuclear receptor of the thyroid hormone.
Elevated serum thyroxine (T4) and nonsuppressed serum thyroid-stimulating hormone, which is inappropriate in context of the elevated T4 and triiodothyronine (T3). Clinically euthyroid or hypothyroid.
Goiter is common. Delayed speech development, mental retardation, and delayed skeletal maturation represent subtle signs of hypothyroidism. Florid clinical signs and symptoms of hypothyroidism are unusual. Attention deficit disorder is common. Treatment is not required for except in the presence of growth retardation or delayed skeletal maturation. The condition should be distinguished from a primary pituitary thyroid-stimulating hormone-secreting tumor.
Precautions before anesthesia
Examine for signs of clinical hypothyroidism and hyperthyroidism. Consider ECG in presence of bradycardia or history suggestive of dysrhythmia. Review and continue current drug therapy perioperatively. Review thyroid function.
Euthyroid patients should not cause great concern; however, the possibility of differential resistance to thyroxine between tissues exists. The occurrence of tachydysrhythmias under anesthesia may represent hyperthyroid effects on cardiac muscle requiring beta blockade. Overt clinical hypothyroidism (or hyperthyroidism) should be controlled in consultation with an endocrinologist prior to anesthesia. Regional anesthesia may be useful when the procedure permits. Close postoperative follow-up of thyroid and parathyroid function is recommended.
Esmolol is probably the perioperative beta blocker of choice if signs of hyperthyroidism develop.
Other conditions to be considered
☞Allan-Herndon-Dudley Syndrome: Syndrome caused by a thyroid hormone cell membrane transport defect due to a mutation in the Monocarboxylate transporter 8 (MCT8) gene. Severe psychomotor retardation (spastic quadriplegia; not walking or rarely ataxic gait; no speech or dysarthria, mental retardation) and low BMI. Laboratory findings include: High T3, low serum reverse T3 (rT3), and T4, normal or slightly elevated TSH.
Dumitrescu Syndrome: Autosomal recessive thyroid hormone metabolism defect due to a mutation in the SBP2 (SECISBP2) gene leading to a selenocysteine insertion sequence binding protein 2 (SBP2) defect. Patients have growth retardation, myopathy, immune deficiency, and photosensitivity. Laboratory findings include: high T4 and rT3, low T3, normal or slightly elevated TSH.