Sitagliptin is a dipeptidyl peptidase-4 inhibitor commonly used in the treatment of type 2 diabetes mellitus for glycaemic control. Concerns have arisen regarding adverse events caused by this drug, particularly concerning arthralgias. Here, we report on a 56-year-old man being treated with sitagliptin who developed inflammatory arthritis after taking the drug for 6 months. The patient presented with pain, swelling and erythema in multiple joints and was eventually diagnosed with seronegative rheumatoid arthritis (RA) under the 2010 American College of Rheumatology/European League Against Rheumatism classification criteria. His symptoms continued for several months after stopping sitagliptin and eventually went into remission after a tapered course of steroids, hydroxychloroquine and methotrexate. Furthermore, the patient is HLA-DRB3 positive, a genetic marker that is still being investigated for its role in the pathogenesis of RA and that may have been a predisposing factor in the development of this patient’s inflammatory arthropathy.

A 67-year-old female with a past medical history of multiple endocrine issues presented for follow-up subsequent to abnormal routine blood testing results. These included low thyroid stimulating hormone (TSH), low parathyroid hormone (PTH), and mildly elevated calcium levels. The presence of hypercalcemia and accompanying low PTH raised the concern for malignancy, while the depressed TSH indicated hyperthyroidism. Review of the patient’s medications revealed daily supplementation with 5 mg of vitamin B7 (biotin). The biotin was discontinued after suspecting the supplement was interfering with the patient's lab values. The labs were repeated one month later. The results showed normalized TSH, PTH, and calcium levels. The increasingly wide-spread use of biotin supplementation and the use of biotin as a component in many of the most common clinical assays has led to a trend of lab errors due to biotin interference. While some physicians are aware of the possibility of skewed results, steps need to be taken to prevent misdiagnosis. This includes ensuring that information about this issue is more widely disseminated, accurately accounting for a patient’s supplement use, reconciling proper clinical correlation with lab results, and promptly reporting when biotin is determined to be the cause of otherwise unexplained lab errors.

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