Thyroid Disease

Key considerations for people living with HIV

There are few data about the effects of HIV infection on thyroid function. However, there is some evidence to suggest that an increasing number of patients taking antiretroviral drugs are presenting with thyroid disorders.¹ Abnormal thyroid function test results are common among patients with HIV, and retrospective analyses have revealed a higher than expected incidence of hypothyroidism in large cohorts of HIV-infected individuals (3.4 per 10,000 patient-years for hyperthyroidism and 10.7 per 10,000 patient-years for hypothyroidism)¹, although this is not a consistent finding. Furthermore, specific patterns of abnormal thyroid function test findings are more frequently identified among patients with HIV. 



However, when compared with the general population, the prevalence of thyroid disease does not always appear to be significantly increased in patients with HIV.^1,2 


Role of the thyroid gland

In healthy individuals, the thyroid produces two important hormones, thyroxine (T­4) and triiodothyronine (T3), that are released into the circulation. These thyroid-derived hormones influence:

• growth
• metabolism
• brain function
• neural development
• dentition
• bone development

   

On average, a normal individual will produce approximately 90–100 μg of T4 and 30–35 μg of T3 per day. T3 is the more biologically active form of the hormone, approximately 80% of which is derived from peripheral metabolism (5’-monodeiodination) of T4 in tissues including the thyroid, pituitary, liver, and kidney.³


Thyroid dysfunction

Imbalances in the production of thyroid hormones are frequently a result of dysfunction of the thyroid gland itself (primary disease); however, abnormalities in hormone production can be stimulated by the pituitary gland, (responsible for the production of thyroid-stimulating hormone [TSH]), or the hypothalamus (which regulates the pituitary gland via thyrotropin-releasing hormone [TRH]). TRH and TSH are critical to thyroid homeostasis.


Implications in patients living with HIV

As treatment options for patients experiencing hypo- or hyperthyroidism are, in general, limited to hormone replacement or removal/counteraction of the thyroid respectively, there are very few additional options to tailor treatment among patients with HIV. However, recent evidence suggests that some antiretroviral therapies may interfere with thyroid hormone replacement therapy,^4-5 and therefore careful observation may be required when these disease states are being treated together.






References

1. Nelson M, Powles T, Zeitlin A, et al. Thyroid Dysfunction and Relationship to Antiretroviral Therapy in HIV-Positive Individuals in the HAART Era. J Acquir Immune Defic Syndr.2009;50(1):113–114.
2. Hoffmann CJ, Brown TT. Thyroid function abnormalities in HIV-infected patients. Clin Infect Dis.2007;45(4): 488-494. 
3. Demers LM. Thyroid disease: pathophysiology and diagnosis. Clin Lab Med. 2004;24(1):19–28.
4. Lanzafame M, Trevenzoli M, Faggian F, et al. Interaction between levothyroxine and indinavir in a patient with HIV infection. Infection. 2002;30(1):54-55.
5. Touzot M, Beller CL, Touzot F, Louet AL, Piketty C. Dramatic interaction between levothyroxine and lopinavir/ritonavir in a HIV-infected patient. AIDS. 2006;20(8):1210-1212.