https://www.selleckchem.com/products/Abitrexate.html Human herpesvirus 6 (HHV-6) infection is the cause of roseola infantum in children. The reactivation of HHV-6 is associated with multiple clinical syndromes including encephalitis and myelitis, especially in haematopoietic stem cell transplant recipients. However, the virus can cause encephalitis in other immunosuppressed as well as immunocompetent individuals. We report a case of a 70-year-old woman who was immunocompromised secondary to treatment of rheumatoid arthritis with leflunomide and methotrexate. The patient presented with acute ataxia, diplopia and dysarthria. MRI brain showed an enhancing lesion in the midbrain. The diagnosis of HHV-6 encephalitis was made after HHV-6 A DNA was detected in both serum and cerebrospinal fluid. Treatment consisted of a 3-week course of intravenous ganciclovir along with physiotherapy. At a 3-month follow-up, repeat MRI brain showed a decrease in size and oedema of the lesion and the patient's neurological function was improved. © BMJ Publishing Group Limited 2020. No commercial re-use. See rights and permissions. Published by BMJ.Lactic acidosis (LA) is characterised by persistently increased blood lactate >5 mmol/L. Type A LA due to anaerobic glycolysis is frequently seen during management of haematological malignancies. A rare form of LA known as type B LA, which occurs as a result of metabolic dysregulation at cellular level has been described recently. This has been reported to be because of Warburg effect (WE) or aerobic glycolysis, which is seen in cancerous cells as they rely on aerobic glycolysis rather than oxidative phosphorylation for energy generation. Presence of type B LA at initial presentation of haematological malignancies is a poor prognosticating factor and has rarely been reported in children. We present a child with T cell acute lymphoblastic leukaemia with mild phenotype of type B LA due to WE. She responded dramatically to definitive chemotherapy an