A sequela, pronounced “seh-KWELL-ah,” is a medical term describing a pathological condition that results from a prior disease, injury, or trauma. Derived from the Latin word meaning “sequel,” it indicates a consequence that follows an event. In a clinical context, a sequela is the residual effect left behind after the acute phase of the original health issue has ended. This means the current condition is a direct, long-term consequence of a past, resolved event.
Defining the Medical Term Sequela
A defining characteristic of a sequela is its nature as a residual effect that persists after the primary causative event is no longer active. The original disease or injury may have fully run its course, been successfully treated, or otherwise resolved, but it leaves behind lasting damage or altered function. The concept hinges on a clear chain of causation, where the residual condition is directly linked back to the resolved primary condition. Sequelae can manifest as physical, psychological, or physiological changes, and their severity can range from minor and temporary to severe and permanent.
Common Examples of Sequela
Sequelae can arise from a wide range of initial events, including infections, traumatic injuries, and chronic conditions. For instance, a person who suffers a severe burn may fully heal from the initial injury, but the resulting scar tissue formation on the skin is considered a sequela. This scar represents a permanent alteration of tissue structure directly caused by the original thermal trauma.
Neurological events often result in prominent sequelae, such as the speech impairment or hemiplegia (paralysis on one side of the body) that can follow a stroke. The damage to the brain tissue from the stroke is the initial event, and the persistent motor or communication deficits are the resulting long-term conditions. Chronic headaches or cognitive deficits are also recognized sequelae of a past traumatic brain injury.
Infectious diseases also leave behind sequelae, most notably “Long COVID,” which is medically referred to as Post-Acute Sequelae of SARS-CoV-2 Infection (PASC). These post-acute effects include persistent fatigue, shortness of breath, and “brain fog” that continue long after the body has cleared the active viral infection. Another historical example involves rheumatic fever, where the bacterial infection’s sequela is often damage to the heart valves, resulting in chronic heart disease.
Sequela Versus Complication and Symptom
The concept of a sequela is often confused with both symptoms and complications, but the distinctions are based primarily on timing and relationship to the active disease process. A symptom is a subjective or objective manifestation that occurs during the active phase of the primary illness. For example, a fever, cough, or sore throat are symptoms that signal the body is currently experiencing an active infection.
A complication, by contrast, is a new problem that arises during the course of an ongoing illness or treatment, often interrupting the healing process or worsening the prognosis. If a patient with the flu develops bacterial pneumonia while they are still actively ill, the pneumonia is a complication because it occurred while the primary illness was still in its acute phase.
The fundamental difference for a sequela is that it occurs after the acute phase of the original condition has terminated or healed. The original cause is no longer present, but its destructive consequences remain, making the sequela a residual condition. This temporal distinction means that while a complication occurs alongside the original disease, a sequela is the lasting aftermath that follows it.