A stroke occurs when blood flow to a part of the brain is disrupted, causing brain cells to die and resulting in a sudden loss of neurological function. The two primary types are ischemic (a blockage) and hemorrhagic (a burst blood vessel). Strokes in young adults (those in their 20s) are relatively uncommon, accounting for about 10% to 15% of all cases, though the incidence is increasing globally. The underlying causes in this age group are often highly specific and differ significantly from those seen in older adults. In many young adult cases, the cause remains undetermined even after extensive testing, classified as a cryptogenic stroke.
Structural and Vascular Anomalies
Physical defects and abnormalities within the circulatory system are among the most frequent causes of stroke in young adults. These structural issues can involve the arteries leading to the brain or the internal structure of the heart. The most common cause of ischemic stroke in this demographic is a tear in the wall of a neck artery, known as a cervical artery dissection.
This dissection involves a small tear in the inner lining of the carotid or vertebral arteries, allowing blood to enter the vessel wall and form a clot. The resulting blood clot can either block the artery at the site of the tear or, more commonly, fragments can break off and travel to the brain, causing an ischemic stroke. These tears can happen spontaneously or follow a minor mechanical trigger, such as whiplash, vigorous exercise, or sudden neck movement.
Structural defects in the heart, specifically a Patent Foramen Ovale (PFO), are another mechanism. These are small holes between the heart’s right and left atria that failed to close completely after birth. A PFO can enable a paradoxical embolism, where a blood clot originating in the venous system passes through the PFO to the arterial circulation and travels to the brain. This mechanism is strongly associated with cryptogenic strokes in young adults.
Malformations or fragile blood vessels are causes. Arteriovenous Malformations (AVMs) are tangles of abnormal blood vessels where arteries connect directly to veins. This structure lacks the normal muscular layer, leading to high pressure that can cause the vessel wall to rupture, resulting in a hemorrhagic stroke. An intracranial aneurysm is an abnormal ballooning of a blood vessel that can rupture and cause a sudden hemorrhagic stroke.
Moyamoya disease involves the narrowing of the distal internal carotid arteries and their main branches. To compensate for the reduced blood flow, a fragile network of small collateral vessels develops, resembling a “puff of smoke” on imaging. This reduced flow often leads to ischemic strokes in younger patients, while the fragility of the new vessels can also cause hemorrhagic strokes.
Blood Clotting and Autoimmune Disorders
Systemic conditions that affect the blood’s ability to clot or cause inflammation in the vessel walls pose a significant stroke risk for young adults. Hypercoagulable states (thrombophilias) are genetic or acquired disorders that increase blood clot formation. Inherited conditions like Factor V Leiden mutation make a clotting factor resistant to natural deactivation, while deficiencies in natural anticoagulants like Protein C and Protein S can also elevate the risk of an ischemic stroke.
The risk associated with these inherited conditions is amplified when combined with factors like PFO or hormonal contraceptives. The most common acquired disorder is Antiphospholipid Syndrome (APS), an autoimmune condition where the body mistakenly produces antibodies that target specific plasma proteins. These antibodies trigger a procoagulant state, significantly raising the risk of both arterial and venous thrombosis, and APS is estimated to be associated with up to 20% of strokes in patients under 45.
Autoimmune diseases, such as Systemic Lupus Erythematosus (SLE), can increase stroke risk through mechanisms including coexisting APS or accelerated atherosclerosis. A more direct cause is central nervous system (CNS) vasculitis, an inflammatory process where the immune system attacks the blood vessel walls. This inflammation causes the vessels to narrow or become blocked, directly leading to an ischemic stroke.
Sickle Cell Disease (SCD) causes stroke in young adults, with approximately a quarter of patients experiencing a stroke by age 45. The abnormal, crescent-shaped red blood cells can block blood flow, causing ischemic stroke. While ischemic events are more common in childhood, the incidence of hemorrhagic stroke rises among adults in their 20s, likely due to a progressive weakening of the cerebral vessel walls.
Acquired Risks and External Factors
External influences and lifestyle choices can trigger stroke events in young adults with underlying susceptibilities. The use of illicit stimulants like cocaine and amphetamines is linked to both ischemic and hemorrhagic stroke. These drugs can cause acute, severe spikes in blood pressure, leading to hemorrhagic stroke, or they can induce cerebral vasospasm, a sudden narrowing of blood vessels that restricts blood flow and causes an ischemic stroke.
Infective Endocarditis (IE), a bacterial infection of the heart valves, can present initially as a stroke in young patients. IE causes the formation of septic vegetations that break off and travel to the brain, blocking blood flow and causing an embolic ischemic stroke. This is particularly relevant in young adults with a history of intravenous drug use, as it increases the risk of IE.
Migraine with aura is an important risk factor for ischemic stroke in young women, even without other risk factors. This risk is significantly magnified when combined with the use of combined hormonal contraceptives (CHCs), which contain estrogen. The estrogen component of CHCs increases the production of clotting factors, making the blood more prone to clotting. This combination can increase the risk of ischemic stroke by as much as six-fold.
Fibromuscular Dysplasia (FMD) is a non-inflammatory vascular disorder. FMD causes abnormal growth in the arterial walls, resulting in a characteristic “string-of-beads” appearance due to alternating areas of narrowing and ballooning. FMD most commonly affects the renal and carotid arteries, and it can predispose a young adult to a stroke by leading to a cervical artery dissection or the formation of an aneurysm.