Myxoedema coma following commencement of anti-TNF therapy and tuberculosis prophylaxis in a patient with RA and latent tuberculosis infection

A 67-year-old man with an 8-year history of seropositive rheumatoid arthritis (RA) on conventional synthetic disease-modifying antirheumatic drug (csDMARD) and history of hypertension and bilateral total knee replacement done 2 years ago presented with active arthritis. He was advised to switch to a biological DMARD etanercept (tumour necrosis factor inhibitor (TNFi)). For this reason, screening tests for latent tuberculosis, hepatitis B and hepatitis C were performed. His chest X-ray showed a fibrotic lesion in the left upper zone and his Mantoux test was positive. He was commenced on etanercept biosimilar along with rifampicin and isoniazid for latent tuberculosis infection. Two days after the commencement of this treatment, the patient developed a loss of appetite and somnolence. His condition progressively deteriorated culminating in a comatose state at the end of 1 week when he had to be hospitalised. There was no history of headache, vomiting, fever, seizures, slurring of speech, weakness of limbs or skin rash. Examination revealed hypothermia (96.2 ° F), bradycardia (44/min), a respiratory rate of 14/min, hypotension (90/54 mm Hg) and low SpO2 (88% on room air). Respiratory, cardiovascular and abdominal examinations were unremarkable. The patient was drowsy but arousable. Deep tendon reflexes showed delayed relaxation. His Glasgow Coma Scale was 8/15 (E2 V2 M4). He had multiple rheumatoid nodules on the extensor aspect of both the elbows and subluxation of multiple metacarpophalangeals with swan-neck and boutonniere deformities and Z-deformity of both the thumbs.