Fever of unknown origin as the major manifestation of subacute thyroiditis

Abstract

Summary Fever of unknown origin is a commonly encountered medical problem. Most common causes include infections, malignancy, and connective tissue diseases. Endocrine causes are rare but are well documented. While fever is common in some endocrine disorders, fever of unknown origin as the sole presenting feature is very rare. We describe a case report of a 63-year-old male who presents with fever of unknown origin. Imaging and biopsy results confirmed the diagnosis of subacute thyroiditis. He was started on prednisone with a good response. We conclude that subacute thyroiditis should be considered in the work up of fever of unknown origin even in the absence of classical signs and symptoms. Learning points Fever of unknown origin is a rare sole presentation of subacute thyroiditis. The classic signs and symptoms may not be manifest at the time of presentation. Normal thyroid function tests and elevated markers of inflammation often make infections, malignancy and autoinflammatory conditions the prime consideration. Imaging of the thyroid gland may point to a morphologic aberration and prompt a thyroid biopsy. After exclusion of infection, a rapid response to steroids may be both diagnostic and therapeutic.

Subacute Thyroiditis Masquerading as Fever of Unknown Origin

“…FUO is defined as a temperature of at least 38.3°C for at least three weeks with an unknown diagnosis after an extensive workup for at least one week [ 1 ]. FUO can be caused by viral, bacterial, and fungal infections as well as rheumatic, malignant, and inflammatory conditions [ 1 ], and thyroid disease is a rare etiology for FUO [ 2 ]. SAT is a relatively uncommon diagnosis with an incidence of 12.1 per 100,000 per year [ 3 ].…”

“…The relative hyperthyroid state is followed by a period of hypothyroidism which can last up to six months and infrequently can be permanent, but most patients return to a euthyroid state [ 4 , 9 ]. Anti-thyroid peroxidase and anti-thyroglobulin antibodies are generally low, and thyroglobulin is elevated [ 1 , 8 ].…”

“…Other distinguishing features in favor of SAT include absent or low anti-thyroid peroxidase antibody and anti-thyroglobulin antibody, but thyroglobulin may be elevated. In SAT, ultrasound with Doppler usually reveals gland enlargement with diffuse or focal hypoechoic lesions and hypovascularity and depressed radioactive iodine uptake on radioactive iodine imaging [ 1 , 9 ]. On the other hand, Graves' disease is marked by a positive thyroid-stimulating antibody, hypervascularity of the thyroid gland on Doppler ultrasound, and diffuse enhancement in radioactive iodine uptake [ 4 , 8 ].…”

“…Fever of unknown origin (FUO) is commonly caused by infections, malignancy, or autoimmune diseases. Endocrine pathologies such as subacute thyroiditis (SAT) are an unusual but significant cause of FUO [ 1 , 2 ]. SAT, also known as de Quervain thyroiditis, stands out as an inflammatory variant usually associated with respiratory viral illnesses, contributing to its non-suppurative nature [ 1 ].…”

“…The incidence of the disease is 12.1 per 100,000 and predominantly affects females, with the highest incidence observed in the 30-40-year age group [ 3 ]. This disorder presents a clinical challenge, particularly in cases where it deviates from the typical course, and it usually presents with painful and tender anterior neck swelling in 70-90% of cases [ 1 ]. The hallmark of SAT is the transient nature of thyroid dysfunction, initiating with hyperthyroidism that persists for several weeks, followed by a phase of euthyroidism, and eventually transitioning into a hypothyroid state.…”