Paroxysmal

The word signals episodicity, which is often the key diagnostic feature. In pertussis the paroxysmal stage brings repeated staccato coughing fits within a single expiration, followed by a forced inspiration through a narrowed glottis producing the whoop, and often post-tussive emesis; infants may present with apnoea and no whoop at all. Elsewhere in medicine the term names paroxysmal supraventricular tachycardia, which starts and stops abruptly and is usually AV nodal reentrant; paroxysmal atrial fibrillation, defined as terminating spontaneously within seven days; paroxysmal nocturnal dyspnoea in heart failure, waking the patient one to two hours after lying down; paroxysmal nocturnal haemoglobinuria, in which a PIGA mutation removes GPI-anchored CD55 and CD59 and permits complement-mediated intravascular haemolysis with thrombosis, treated with eculizumab; and the paroxysmal hypertensive episodes of phaeochromocytoma with headache, palpitations, and diaphoresis. In all of these, the return to a normal baseline between attacks is what distinguishes paroxysmal from persistent disease.