Paroxysmal

Paroxysmal is an adjective used to describe events that begin suddenly and occur in abrupt, transient episodes. The term derives from the Greek paroxysmos meaning a sharp or sudden attack and entered English through Latin; it is related to paroxysm, an abrupt outbreak or fit.

In clinical contexts, paroxysmal denotes events that have a sudden onset and are typically episodic or intermittent rather than persistent. Conditions described as paroxysmal may remit spontaneously or terminate after minutes, hours, or days. The descriptor is often used to distinguish episodic forms from chronic or continuous states.

Common examples include paroxysmal atrial fibrillation, in which episodes of irregular heartbeat begin abruptly and revert to normal rhythm without ongoing rhythm disturbance between episodes; paroxysmal nocturnal dyspnea, sudden nighttime shortness of breath that improves upon waking or upright positioning; and paroxysmal pain or movement disorders that occur in sudden attacks. In neurology, paroxysmal events may refer to sudden bursts of abnormal electrical activity, such as paroxysmal depolarization shifts associated with seizures. Paroxysmal nocturnal hemoglobinuria is a hematologic condition named for hemolytic episodes that can occur in the night or morning.

The term does not specify a mechanism, duration, or frequency by itself; it simply marks a pattern of abrupt, episodic onset. This versatility makes paroxysmal a common descriptor across specialties.