Subacute thyroiditis following Mpox infection in a patient with human immunodeficiency virus.

Summary: Mpox (MPX) formerly known as monkeypox was declared a public health emergency of international concern, following an outbreak that commenced in May 2022. We report a case of subacute thyroiditis following MPX infection. To our knowledge, it is the first documented incidence of this complication in humans. A 51-year-old male, with a well-controlled human immunodeficiency virus (HIV) infection on antiretroviral therapy, was reviewed 3 weeks after a positive test for MPX. The acute skin lesions and initial systemic symptoms had resolved, but he described significant neck discomfort, fatigue, weight loss and night sweats. Blood tests showed a raised C-reactive protein, free T4 and suppressed thyroid-stimulating hormone. His thyroid antibodies were negative. He was treated initially with carbimazole and propranolol, pending exclusion of any other intercurrent infection. A chest radiograph was normal; blood cultures and a combined nose and throat swab for respiratory virus PCR testing were negative. Following this, he commenced a 2-week course of prednisolone; his symptoms resolved completely within 24 h of starting. He subsequently developed hypothyroidism, which was treated with levothyroxine. The clinical features, abnormal thyroid function, raised CRP and negative thyroid antibodies 3 weeks post-MPX positive test was consistent with viral subacute thyroiditis. This case demonstrates that, as described following other viral infections, MPX can cause subacute thyroiditis, which follows a similar course to the classic form of subacute thyroiditis. Clinicians should be aware of this potential endocrine complication when attending to patients with MPX. Learning points: Subacute thyroiditis can present following mpox virus infection. Its course is similar to the classic form of subacute thyroiditis and steroids are effective. It is important to exclude other concurrent infections prior to starting steroids, especially for patients who are immunosuppressed or in other high-risk groups.