Hypothyroidism and Diabetes Mellitus
G. V. Prabhu
Diabetes mellitus and thyroid dysfunction are the two most commonly occurring endocrine disorders. The prevalence of thyroid dysfunction in patients with type 1 diabetes have been reported to be as high as 29% and can lead to loss of glycemic control, disturbance of cognitive function and/ or fatigue. In patients with type 2 diabetes, hypothyroidism may interfere with weight loss, and thyroid hormone therapy may be beneficial for weight management. Obese and elderly patients should be screened for thyroid dysfunction and tested every 5 years in the absence of symptoms of thyroid dysfunction. Thyroid hormone therapy should be initiated as appropriate giving credence to TSH levels, symptomatology, age and cardiovascular status
Diabetes mellitus (DM) is the second most commonly occurring endocrine disorder with thyroid dysfunction. Patients with Type 1 Diabetes Mellitus or insulin dependent diabetes mellitus may have coexisting thyroid disease, thyroid specific antibodies, and/or evidence of polyglandular endocrinopathy (such as anti-islet cell antibodies, anti-insulin antibodies and antibodies to other endocrine organs).
Type 1 diabetes is an intrinsic part of the polyglandular autoimmune group of diseases. The high prevalence of thyroid disease and a presence of anti-thyroid antibodies in a patient with type 1 diabetes was reported by McKenna and associates in a study of 371 children and adolescents. Elevation in serum concentrations of thyroid stimulating hormone(TSH) with a normal T4 have been reported by Genuth in approximately 12% of patients with type 1 diabetes upon screening.
In addition, antibodies to glutamic acid decarboxylase (GAD), the 64-kd islet cell protein, also seem to develop in patients with both type 1 diabetes and autoimmune thyroid disease. One study by Kawasaki and associates reported that patients with type 1 diabetes who also had autoimmune thyroid disease had high concentrations of GAD antibodies. This raises the possibility that in some way the presence of autoimmune thyroid disease may influence the development or activity of the diabetes mellitus.
Studies have shown that adults with diabetes mellitus, initially presenting with type 2 diabetes, can become frankly insulin dependent, possibly due to autoimmune destruction of the islet cells. These patients, perhaps as high as 15% to 20% of the type 2 diabetes population, have an increased prevalence of GAD antibodies in their serum and may be considered to have a latent autoimmune diabetes in adults (LADA) with an etiology similar to type 1 diabetes.
Effects of hypothyroidism in patients with type 1 diabetes.
We may see loss of glycemic control, disturbance of cognitive function, and/or fatigue, all of which can be corrected with thyroid hormone replacement therapy.
Type 2 diabetes and thyroid function:
Often patients with type 2 diabetes are significantly overweight. Patients with Type 2 diabetes with hypothyroidism find it difficult to lose weight, possibly because of reduction in the basal metabolic rate. When such patients are put on insulin or an oral anti-diabetic medication (e.g. sulphonylureas) the end result may actually be weight gain. The unrecognised hypothyroidism may be part of the problem for their failure to lose weight.
Screening of patients with diabetes mellitus for the presence of thyroid dysfuncion:
In the case of patients with diabetes, factors other than infection and noncompliance with insulin therapy contribute to loss of glycemic control. This may be due to (abnormal thyroid function which can have profound effects on blood glucose control in these patients with diabetes. Hypothyroidism and hyperthyroidism can possibly coexist and patients need to be screened for these.
- Therefore, for patients with type 1 diabetes usually screen for serum concentrations of TSH and free T4 (thyroxine) on the first visit.
- Children of any age, who do not gain weight or add muscle adequately, should also be evaluated. Adolescents need to be screened as well.
- In particular, young women with diabetes and delayed menarche should be screened to determine whether this dysfunction is due to delayed ovarian function or autoimmune disease.
- In addition, in obese and/or elderly patients with type 2 diabetes, screening for thyroid disease should be performed on the first visit because of high incidence of hypothyroidism in these groups.
Management Strategies For Patients With Diabetes Mellitus And Thyroid Dysfunction
If the patient has appropriate clinical symptoms and signs, initial therapy should be started immediately with a low dosage of thyroxine and subsequently titrated higher.
If the serum TSH level is borderline (between 5 and 10 units per millilitre U/ml), it may be appropriate to initiate therapy. Treatment is influenced by the symptomatology and by the presence of anti-thyroid peroxidase antibodies.
If the TSH level is above 10U/ml or there are elevated levels of anti-microsomal and anti-thyroid antibodies, then initiate thyroid hormone therapy regardless of the symptomatology
In a younger patient with no evidence of any cardiovascular disease, full physiologic replacement with a dose approximately 1.6 to 1.8 microgram per kilogram per day (mcg/kg/day), initiating therapy with 75mcg or 100 mcg of levothyroxine per day depending on the body weight. In an older patient over 60 years of age or a patient with a cardiovascular disease, a more cautious administration of thyroid hormone is done normally starting with a dosage of 25 mcg per day with dose increments every 3 weeks thereafter until the TSH concentration is in the normal range. In a patient with angina, an initial daily dosage of 12.5mcg per day would be appropriate, followed by gradual dose increments every 4 to 6 weeks depending on cardiac symptoms and serum TSH response.
- Diabetes mellitus and thyroid dysfunctions are the two most commonly occurring endocrine disorders.
- Anti-thyroid antibodies have been reported in approximately 19% of children and adolescents with type 1 diabetes.
- The prevalence of thyroid dysfunctions in patients with type 1 diabetes have been reported to be as high as 29%.
- In patients with type 1 diabetes, hypothyroidism can lead to loss of glycemic control, disturbance of cognitive function and/ or fatigue.
- In patients with type 2 diabetes, hypothyroidism may interfere with weight loss and the administration of insulin and oral antidiabetic drugs e.g. sulphonylureas, can actually result in weight gain. Thyroid hormone therapy may be beneficial for weight management.
- Patients with type 1 diabetes should be screened for thyroid dysfunction by measuring serum concentrations of TSH and free T4
- Obese and elderly patients should be screened for thyroid dysfunction.
- If the initial screening results are negative, patient should be tested every 5 years in the absence of symptoms of thyroid dysfunction.
- Thyroid hormone therapy should be initiated in the following:
- In a patient with serum TSH concentrations >10 U/ml.
- In symptomatic patients with border- line elevations of serum TSH between 5 to 10 U/ml.
- Thyroid hormone replacement dosage should be 75mcg or 100mcg per day in younger patients with no evidence of cardiovascular disease.
- Thyroid hormone replacement dosage should be at 25 mcg per day in patients >60 years of age, with dosage increments of 25mcg per day every 3 weeks until the serum TSH concentration is within normal limits.
- McKenna M J,Herskowitz R,Wolfsdorf JI. Screen- ing for thyroid disease in children with Type 1 diabetes. Diabetes Care,1990; 13:801-803.
- Genuth SM. Associations between diabetes and other endocrine disorders. CII in Diabetes, 1990;8:81-90.
- Kawasaki E, Takino H, Yano M, et al. Autoantibodies to glutamic acid decarboxylase in patients with type 1 diabetes and autoimmune thyroid disease. Diabetes.1994:43;80-86.
- Gerstein H C, Incidence of postpartum thyroid dysfunction in patients with Type 1 diabetes mellitus. Ann. Intern med. 1993:118:419-423.
- Jackson I & Krosnick A, Thyroid update No.10. The interrelationship between diabetes mellitus and thyroid dysfunction.