Dr. Sanjay Kalra discusses the correlation between diabetes and hypothyroidism, underscoring the need for vigilance in screening and comprehensive pharmacological management to deliver optimum outcome.

The physiology of all endocrine glands is intricately connected with each other. These links and correlations are visible in clinical medicine as well. Endocrine function of a particular gland influences the screening, diagnosis, clinical features, natural history and management of diseases of other endocrine organs as well. This forms the noesis of the science of glucocrinology.

Two of the commonest endocrine illnesses encountered in clinical practice are diabetes mellitus and thyroid disorders. The multifaceted interactions between thyroid function and glycaemic metabolism, and thyroid disease and dysglycaemia, form the subject matter of thyro-diabetology.

Clinical features

The symptoms of type 2 diabetes and hypothyroidism, as well as type 1 diabetes and hyperthyroidism, may overlap each other. Easy fatiguability, weight gain, symptoms of neuropathy and myopathy may occur in both type 2 diabetes and hypothyroidism. Type 1 diabetes and hyperthyroidism may present with weight loss, tiredness, and skin lesions.

Both diseases may occur together, and as part of a wider spectrum of disease. Autoimmune polyglandular endocrine syndromes are one example of such a presentation. Some conditions such as obstructive sleep apnoea, polycystic ovary syndrome, and non-alcoholic fatty liver disease may be mimicked by, or precipitated by, both diabetes and hypothyroidism.

The occurrence of hypothyroidism may lead to hypoglycaemia in a person with hitherto stable glycaemic levels. As a corollary, uncontrolled hyperthyroidism may be a cause of refractory hyperglycaemia. Poorly complications may lead to poor absorption of drugs, which may impair efforts to manage thyroid disease.

Investigations

Acute illness can alter thyroid function tests (sick euthyroid syndrome). A low T3 & or T4, with or without a low TSH, in persons with acute complications of diabetes, such as metabolic crisis or infection, should be interpreted with caution. A repeat test may be required once the acute comorbidity has been resolved.

Similarly, HbA1c levels may provide a misleading idea of glucose control in uncontrolled hypothyroidism, due to alterations in red blood cell production and turnover.

Drugs

Many glucose lowering drugs can influence thyroid function. Metformin can reduce TSH levels, older sulfonylureas may exhibit goitrogenic effect, and pioglitazone can cause periorbital oedema. Liraglutide is contraindicated in persons with a history of, or family history of medullary thyroid carcinoma. It would be prudent practice to check TSH prior to, and a few months after initiating long term glucagon-like peptide 1 receptor agonist (GLP1RA) therapy.

Corticosteroids, sometimes used in thyroid management, can cause hyperglycaemia. Beta blockers, used as adjuvant therapy in Graves’ disease, can be associated with fatiguability and erectile dysfunction.

Pragmatic suggestions

All persons with type 1 diabetes must be screened, at diagnosis and annually, for thyroid dysfunction. Serum TSH should suffice in most patients. Estimation of serum T3, T4 and TSH is indicated where central hypothyroidism is suspected, e.g., in short stature. Thyroid antibodies may need to be evaluated where thyroid hormone assay reports are equivocal or are discordant with clinical presentation.

All persons with type 2 diabetes, in whom clinical suspicion of thyroid dysfunction is high, should be screened with a TSH estimation. These situations include persons with poor, erratic, or sudden change in glycaemic control; persistent symptoms despite good glycaemic control; and surrogate markers of hypothyroidism, such as dyslipidaemia and raised liver enzymes.

All persons with thyroid disorders should be screened for dysglycaemia at presentation, and annually. Screening should also be done prior to and after starting corticosteroid therapy. Effective management of hypothyroidism may unmask latent diabetes, and treatment of hyperthyroidism can help in reversal of borderline dysglyycaemia.

To read other articles in this series, click,

Difficult diabetes- The diagnosis is important

Hyperglycemia- Think beyond glucose

Diabetes and the liver- Why this vicious circle needs immediate attention

Diabetes & dermatoses: How to diagnose & treat?

Remission in type 2 diabetes: Dr. Sanjay Kalra

Disclaimer- The views and opinions expressed in the article and videos are those of the speakers and do not necessarily reflect the official policy or position of M3 India.

The author, Dr. Sanjay Kalra is a leading Endocrinologist and the current President of the Endocrine Society of India.