Sub-Acute Thyroiditis Presenting as Pyrexia of Uknown Origin

Abstract

Introduction: Pyrexia of unknown origin (PUO) is often a diagnostic challenge. Common causes currently reported include non-infectious inflammatory disorders (NIID) (30.6%), infections (23.1%), malignancy (10.7%) and miscellaneous (12.4%). However, 23.1% remain undiagnosed despite extensive investigations. Fever is a component of subacute thyroiditis (SAT) in 28-83% of subjects reported in the literature. But its presentation as a PUO is reported only in a handful of subjects. Case Presentation: A 71-year-old Asian male presented with evening fevers of 2-3 weeks duration. He had no accompanying sweats, cough, breathlessness, or weight loss. He had a past history of TB, polio, hydatid cyst and hypertension for which he was on treatment. He was a teetotaler. Several family members living in his native land had active TB and he visited them often. Clinical examination at initial presentation was unremarkable. He interrupted investigations to go back to Asia, and became unwell for over 6 weeks with evening fevers and sweating, a weight loss of over 7 kg, and a poor appetite. At this point he had no neck pain, palpitations or bowel abnormalities. Clinical examination continued to be normal upon his return to the UK and in the Endocrine Clinic. Investigations: Investigations were done to exclude (a) infections - There was no growth of pathogenic organisms in repeated blood, urine and sputum cultures. Screening tests for TB, hepatitis, and glandular fever were negative. Blood screens for malarial parasites, amoebic and Brucella serology, and stools examination and culture were also negative. Echocardiography was normal. (b) Malignancy - Urine Bence Jones proteins and serum protein electrophoresis were normal. Bone marrow examination was suggestive of Leishmaniasis but a PCR test excluded this diagnosis. Humoral markers of malignancy were negative. CT scans of the thorax, abdomen and pelvis were normal and did not show any evidence of visceral abnormalities (c) NIID - CRP 120, ESR 130, with blood tests consistent with iron deficiency. Autoimmune screening for dsDNA, ANA, ANCA were negative. Upon return to the UK a PET/CT scan showed the diffuse tracer uptake in both thyroid lobes and changes consistent with a large left lobe. Free thryroxine was 28pmol/l (reference range 9-19.1), and TSH was undetectable (<0.004 mU/l). Thyrotrophin receptor antibodies were negative. Management and conclusion He was given carbimazole initially but this was stopped as he became severely hypothyroid. This hypothyroidism persisted for several months even after stopping carbimazole but reversed spontaneously. He therefore had a biphasic pattern of thyroiditis typical of SAT. There are only 9 previous cases reported of SAT presenting as PUO. Although SAT is a rare cause of PUO, early thyroid testing and if necessary, functional thyroid imaging should be considered in subjects with PUO to confirm it.