Not all C. diphtheria infections result in toxin production since toxin production depends upon the strain of the bacteria and often whether a phage virus is present. Early administration of antitoxin can prevent the toxin mediated complications. Myocarditis may develop during the second week of illness. Signs and symptoms of myocarditis include congestive heart failure, tachycardia, muffled heart tones, murmurs, and dysrhythmia. Myocardial complications are generally reversible following antibiotic treatment, anti-toxin administration, and eradication of the C. diphtheriae infection.
Neurologic complications appear after varying latent intervals.
Examples include paralysis of the soft palate, oculomotor paresis, dysphagia, diaphragmatic weakness, peripheral neuropathy, etc. Since these complications are largely motor and CSF protein is elevated, these findings are difficult to distinguish from Guillain-Barre syndrome. Rare complications include vascular instability, gastritis, hepatitis, nephritis and hemolytic uremic syndrome. The diagnosis of diphtheria should be made clinically. Material from beneath the white membrane or the membrane itself should be sent for gram stain and culture.