Symptoms develop 10 to 28 days after the onset of respiratory complaints. Two types of neuropathy are seen. The first, cranial nerve involvement, is generally limited to the ninth and 10th nerves, resulting in difficulty swallowing, aspiration, nasal regurgitation, and loss of the gag reflex. Less often, oculomotor and facial nerves become impaired. The second type of neuropathy tends to occur somewhat later in the course of the illness and resembles Guillain-Barr syndrome.
Patients have quadriparesis associated with hyporeflexia.
Degeneration of myelin sheaths and axon cylinders is observed in biopsy specimens. After treatment of the infection, slow but complete neurologic recovery ensues. In the early stages, diphtheria pharyngitis mimics group A streptococcal pharyngitis and mononucleosis. As diphtheria progresses, unlike in these other two diseases, the exudate changes, becoming darker and forming a membrane that cannot be removed without causing bleeding. Neurologic abnormalities, such as ninth and 10th nerve deficits or ECG changes, should also alert the clinician to the possibility of diphtheria.