Pelupessy, J. M., R. Makmur, and D. Daud. “Bull-Neck, Electrocardiographic Changes and Creatine Phosphokinase Blood Levels in Patients With Diphtheria”. Paediatrica Indonesiana, Vol. 31, no. 11-12, Dec. 1991, pp. 303-11, https://paediatricaindonesiana.org/index.php/paediatrica-indonesiana/article/view/1452.