Introduction Discordant thyroid function tests are routinely encountered in clinical practice. Differential diagnoses include acute thyroxine ingestion, laboratory interference from heterophilic antibodies, thyroid hormone resistance, TSH-secreting pituitary adenomas and thyroxine protein binding abnormalities. The impact of abnormal binding proteins may be less recognized since widespread use of free thyroxine assays compared to older total thyroxine assays. Case report A 69-year-old female was referred for assessment of discordant thyroid function tests. Biochemistry since July 2015 showed persistently elevated FT4 levels by immunoassay ranging between 25 to 34 pmol/L with normal or slightly decreased TSH ranging between 0.05 to 2.74 mU/L. The patient was clinically euthyroid on 100 mcg daily of thyroxine for Hashimoto’s thyroiditis. FT4 measured using Liquid Chromatography – Tandem Mass Spectrometry (LC-MS/MS) was 19.5 pmol/L. Exome sequencing (confirmed by Sanger sequencing) detected a guanine to adenine substitution at residue 725 of the ALB gene previously associated with dysalbuminaemic hyperthyroxinaemia. The patient’s daughter had similar thyroid function tests and the same genetic variant. FT4 results from three different automated immunoassays showed the Roche Cobas and Siemens Centaur platforms to be most affected by the variant, and Abbott Architect had the best agreement with LC-MS/MS. Conclusion Familial Dysalbuminaemic Hyperthyroxinaemia is a potential cause of discordant thyroid function tests. Clinicians suspecting protein binding abnormalities may further investigate using reference methods such as LC-MS/MS and equilibrium dialysis if available. The increasing accessibility of exome sequencing offers a cost-effective method of diagnosing genetic variants that cause discordant thyroid function tests.

This case report describes an 84-year-old man who presented with 3 weeks of gradually worsening right arm weakness associated with a painful vesicular rash across his arm. This occurred 3 days after his first dose of the ChAdOx1 nCoV-19/AZD1222 (University of Oxford, AstraZeneca and the Serum Institute of India) vaccine. The diagnosis was complicated by the presence of right C5–C6 foraminal stenosis compressing on the C6 nerve root sheath on non-contrast MRI, leading to an initial diagnosis of cervical radiculopathy. However, a positive varicella zoster virus-PCR test and findings of abnormal contrast enhancement of his right C5–C7 nerve roots on gadolinium-enhanced MRI resulted in a revision of his diagnosis to zoster radiculopathy. He was subsequently commenced on oral valacilovir and made significant recovery. This report aims to highlight the diagnostic dilemma between cervical radiculopathy secondary to spondylosis and zoster radiculopathy and how an erroneous diagnosis could result in inappropriate, aggressive surgical intervention and delayed treatment with antiviral therapy.

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