• congenital hypothyroidism :

Frequency: 1/2,000 to 1/4,000 births. The initial clinical signs are non specific because part of the maternal T4 passes the placental barrier: this is why searching for hypothyroidism is currently part of routine neonatal screening (blood sample between 2 and 7 days of life for the measurement of TSH or T4) in the majority of developed countries. There is a female preponderance of approximately 2:1 boy. Approximately 85 % of cases are sporadic and 15 % are hereditary.

Sporadic cases are generally caused by dysgenesis of the thyroid gland: agenesis or athyreosis, ectopy (lingual thyroid, for example) or hypoplasia.

The most severe form is congenital myxedema caused by athyreosis. In its severe form, the condition often leads to the postmature birth of newborn with a high weight for its size, a wrinkled face and a shiny skin. There is often a delayed emission of meconium, and at the clinical examination, there is usually an umbilical hernia and large fontanels. The infant in whom the diagnosis of hypothyroidism has not been made during the neonatal period (developing countries) presents with: lethargy, feeding problems, constipation, macroglossia, prolonged jaundice, hypotonia, hypothermia. Children with congenital hypothyroidism often have associated cardiac or neurological anomalies.

Some cases of thyroid dysgenesis are associated with a mutation of one of the genes responsible for the synthesis of thyroid hormones: PAX-8, NKX2.1 or NKX2.5 coding for thyroid transcription factors.

Outside of the dysgenesies, other causes of congenital hypothyroidism are:

-        hypothalamic-pituitary insufficiency: anomalies of TSH secretion in hypothalamic or pituitary problems, or malformation of the median line structures  such as in  De Morsier syndrome (see this topic)

-        resistance to TSH (5%): low T4 and high TSH levels

-        resistance to thyroid hormones resulting caused by:

1) a disorder of the intracellular transport of T3: mutation of the MCT8 gene (monocarboxylate carrier 8) located on the X chromosome causing the Allan-Herndon-Dudley syndrome [MIM 300 095] with hypotonia, spastic quadriplegia, mental retardation, epilepsy, ataxia, and signs of hypermetabolism

2) a disorder of the metabolism of thyroid hormones: mutation in the SECISBP2 gene, which codes for SBP2 (selenocysteine insertion sequence binding protein 2) [MIM 607 693]; autosomal recessive transmission: immune deficiency, myopathy, delayed bone maturation, photosensitivity

3) a disorder of the intracellular action of thyroid hormones (nuclear receptor or other):

* mutation of the THRB gene [MIM 185 570; 274 300] that produces Refetoff syndrome (generalized resistance to thyroid hormone) with high free T4 level, tachycardia, goiter and hyperactivity disorders

* mutation of theTHRA gene [MIM 190 120]: low T4/T3 ratio; cognitive disorders , delayed closure of cranial sutures, delay in dental and bone maturation, skeletal dysplasia, macrocephaly, anemia, sometimes seizures

-        a disorder of the hormonosynthese resulting from abnormalities of the genes encoding for the synthesis of various enzymes involved in the production of T3 and T4:

-        lack of uptake of iodin by the thyroid cells;

-        lack of production of hydrogen peroxide due to a mutation in the DUOX2 (dual oxidase 2 or thyroid oxidase 2) or DUOXA2 (dual oxidase maturation factor 2) gene

-        deficiency in thyroid peroxidase, resulting in a failure to organification of iodine; in case of associated deafness:  Pendred syndrome (see this term)

-        non-condensation of the iodothyrosines into iodothyronines;

-        anomaly of proteolysis of thyroglobulin and of the release of T3 and T4;

-        absence of deiodination of the iodothyrosines

The frequency of congenital hypothyroidism is increased in children with trisomy 21, Turner syndrome or homozygous ß-thalassemia. It is also present in the Bamfort and Johansson - Blizzard syndromes (see these terms)

• transient congenital hypothyroidism: in response to

-        maternal hyperthyroidism poorly treated during pregnancy: it lasts several months

-        a deficiency in iodine intake: prematurity

-        transplacental transfer of maternal antithyroid antibodies: it lasts a few weeks

-        an excess of iodine as in case of maternal treatment with amiodarone

-        the presence of a large hepatic hemangioma trapping or consuming a thyroid hormones: reversal after the removal or  regression of the tumor

-        some DUOX1 or DUOX2 gene mutations causing a transient defect in synthesis of hydrogen peroxide

• acquired hypothyroidism :

There are acquired types of hypothyroidism:

-        insufficient iodine intake ('endemic goiter"): very rare since the routine iodine supplementation of dietary salt

-        resulting from an autoimmune thyroiditis, especially in case of trisomy 21

-        following cervical irradiation

-        following a partial or total thyroidectomy,

-        in cystinosis due to excess cystine in the thyroid cells

-        following a tumoral or idiopathic hypothalamic-pituitary insufficiency; half of patients treated with growth hormone have a decrease in the free fraction of T4 and an increase of T3 which globally translates into central hypothyroidism in an apparently euthyroid patient

• mild volume goiter of the adolescent girl : it is due to a relative iodine deficiency at a time of increased needs for thyroid because of puberty. The diagnosis is based on the measurement of iodine (< 10 µg/mL) and this condition responds very well to an increase  dietary intake of iodine.

Untreated congenital or acquired hypothyroidism can lead to :

-        muscle involvement: Kocher-Debré-Sémélaigne syndrome (see this term)

-        precocious pseudopuberty with ovarian hyperstimulation: Van Wyk - Grumbach syndrome (see this term)

Anesthetic implications: 

ensure that the patient is euthyroid and is taking its thyroid opotherapy on the day of the procedure.

Complications of untreated hypothyroidism:

-        myocardial depression with baroreceptor dysfunction, bradycardia

-        hypoventilation,

-        anemia and reduced plasma volume,

-        tendency to hypoglycemia with hyponatremia,

-        disturbance of the metabolic functions of the liver,

-        tracheal compression (and secondary tracheomalacia) if the size of the goiter is important (including plunging/substernal goitre).

In case of urgent operative indication a non-euthyroid patient: risk of heart failure, prevention of hypothermia; slow metabolism of anesthetic agents; monitoring of electrolytes and blood glucose.

There is often an adrenal insufficiency associated with the stress situation or, at least, a decreased adrenocorticotropic response.

References : 

-        Farling PA. 
Thyroid disease. 
Br J Anaesth 2000; 85:15-28

-         Mason KP, Koka BV, Eldregde EA, Fishman SJ, Burrows PE. 
Perioperative considerations in a hypothyroid infant with hepatic hemangioma. 
Pediatr Anesth 2001; 11: 228-31.

-        Mouat F, Evans HM, Cutfield WS t al. 
Massive hepatic hemangioendothelioma and consumptive hypothyroidism. 
J Pediatr Endocrinol Metab 2008; 21: 701.

-         Refetoff S, Bassett JHD, Beck-Peccoz P, Bernal J et al. 
Classification and proposed nomenclature of inherited defects of thyroid hormone action, cell transport and metabolism. 
Thyroid 2014; 3: 1-3

Updated: March 2019