Complications

Complication
Timeframe
Likelihood
short term
low

May occur with a high initial dose of levothyroxine in patients with coronary artery disease.

long term
low

Most likely due to non-adherence, and less often from drug interactions and co-existing illness.

long term
low

May occur with over-treatment.

Acute atrial fibrillation

long term
low

May occur with over-treatment.

Osteoporosis

long term
low

Myxoedema coma is a rare life-threatening state in which severe hypothyroidism markedly worsens.

In general, it occurs in older people and is usually precipitated by an underlying medical illness. The mortality rate associated with myxoedema coma is 25% to 60%.[3][51]

Clinical features include hypothermia, change in mental status, hypotension, bradycardia, hypoventilation, and diffuse non-pitting oedema.[1][3][51]

Patients with myxoedema coma should be treated in the intensive care unit under the supervision of an endocrinologist.

variable
medium

Sub-clinical hypothyroidism or the presence of thyroid antibodies has been found to be associated with an increased risk of complications in pregnancy, such as pre-eclampsia, perinatal mortality, recurrent miscarriage, and fetal neurological maldevelopment.[47]​ There is no good evidence that treatment of sub-clinical hypothyroidism during pregnancy reduces the incidence of these complications.[39][50] However, some experts recommend treating this condition in pregnancy.[29][45]

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