Antiphospholipid syndrome may attack the brain without causing clots

Antiphospholipid syndrome, an autoimmune disorder best known for causing blood clots and pregnancy complications, may be quietly damaging the brains of patients in ways that standard diagnostic workups completely miss. A new review published in Frontiers in Lupus argues that the syndrome’s neurological toll extends far beyond the ischemic stroke that clinicians typically associate with it, encompassing cognitive dysfunction, chorea, headache, and seizures that arise through immune-mediated mechanisms rather than thrombosis alone. The author, Yuichiro Fujieda of Toho University in Tokyo, proposes that these four under-recognized manifestations share a common basis in what he terms neurovascular-immune dysfunction, a process in which antiphospholipid antibodies attack the brain through pathways that conventional MRI and the standard antibody panel cannot detect.

The clinical picture that emerges from cohort studies is striking. Cognitive impairment affects between 11 and 60 percent of patients with antiphospholipid syndrome, migraine occurs in approximately 20 percent, seizures in roughly 7 percent, and chorea in 1.3 percent. Many patients report long-standing functional limitations from these manifestations, independent of any history of ischemic events. Yet in routine clinical evaluation, these symptoms are often not attributed to the syndrome at all. The discrepancy between clinical severity and imaging findings frequently leads to misclassification as idiopathic, functional, or psychiatric disorders, leaving patients without appropriate treatment for years.

The mechanistic core of the review centers on the neurovascular unit, the functional assembly of endothelial cells, pericytes, astrocytic end feet, the basement membrane, neurons, and microglia that maintains blood–brain barrier integrity and couples regional cerebral blood flow to neuronal activity. Under physiological conditions, this assembly preserves an immunologically privileged microenvironment. In antiphospholipid syndrome, antiphospholipid antibodies and associated thrombo-inflammatory mediators act on several of these components at once, so that endothelial activation, barrier breakdown, and glial inflammation reinforce one another rather than occurring in isolation. Antibody-mediated neurotoxicity, microvascular injury, blood–brain barrier disruption, and complement-driven neuroinflammation operate together within this unit, producing a continuum of injury that is not adequately captured by conventional MRI or the standard antibody panel.

Cognitive dysfunction is the most common and often the most disabling of these non-thrombotic manifestations. Patients frequently describe brain fog, slowed thinking, reduced concentration, and difficulty performing everyday tasks, symptoms that fluctuate over time and are often too subtle to be captured by routine cognitive screening such as the Mini-Mental State Examination or the Montreal Cognitive Assessment. Even mild impairment can affect employment, education, and social roles, imposing a sustained reduction in quality of life. The affected domains include executive dysfunction, complex attention, visual reproduction, and learning, supporting a profile of cognitive dysfunction that is not limited to global cognitive decline. Dementia, by contrast, is reported in only 0 to 6 percent of antiphospholipid antibody-positive individuals, considerably less than the frequency of cognitive dysfunction itself.

The risk of cognitive impairment is not uniform across antibody profiles. Reported frequencies are higher in patients who meet the clinical criteria for antiphospholipid syndrome than in asymptomatic carriers, and lupus anticoagulant positivity, high antibody titers, and triple positivity confer the greatest risk. Isolated low-titer or single-antibody positivity carries comparatively lower risk. In antiphospholipid antibody-positive individuals without prior thrombotic or obstetric events, cognitive impairment has been reported at frequencies of 5.9 to 31.1 percent in a systematic review. Several non-thrombotic mechanisms have been implicated. Loss of blood–brain barrier integrity allows antibodies and complement components to reach brain tissue, where they can contribute to local inflammation. The antibodies can target neuronal and glial antigens, and passive transfer of patient-derived antibodies produces cognitive impairment in animal models. In experimental antiphospholipid syndrome, immunization with beta-2 glycoprotein I elevates brain tumor necrosis factor alpha and prostaglandin E, with microglial reactivity in the cortex, parahippocampal region, and hippocampus, accompanied by behavioral hyperactivity. In factor V Leiden mice with experimental antiphospholipid syndrome, the same immunization produces demyelination and axonal loss with impaired learning, attributed to antibody-mediated neurodegeneration.

Chorea, the most characteristic movement disorder of the syndrome, occurs in only 1.3 percent of patients but can be the initial manifestation of the disease. It predominantly affects young women, with a mean age at onset of 21 plus or minus 12 years in the largest series, and shows a particularly strong association with childhood-onset disease, occurring in 14 percent of patients with disease onset before age 15 compared with 1 percent of those with later onset. Hormonal factors appear to contribute, with oral contraceptive use preceding chorea onset in 12 percent of cases and pregnancy or the postpartum period in 8 percent. Several lines of evidence indicate that chorea is not adequately explained by ischemic mechanisms. Conventional brain imaging is often normal or non-specific despite overt chorea, and basal ganglia lesions are rarely demonstrated. Fluorodeoxyglucose positron emission tomography reveals striatal hypermetabolism, suggesting active neural dysfunction rather than tissue loss. Antibodies from pediatric patients with antiphospholipid-related chorea bind to a dopaminergic neuronal cell line, a proof-of-principle finding consistent with a direct antibody–neuron interaction. Dopamine antagonists such as haloperidol provide effective symptomatic control, while glucocorticoids are the most frequently reported treatment for refractory cases, and immunomodulatory agents including intravenous immunoglobulin, plasma exchange, and cyclophosphamide have been used, with rituximab reported effective in therapy-resistant childhood chorea.

Headache, particularly migraine, is among the most frequent non-thrombotic manifestations and is often attributed to a primary headache disorder rather than recognized as a feature of the syndrome. Migraine occurs approximately twice as frequently in female patients as in male patients with the syndrome, at 23 percent versus 12 percent, with onset typically in young adulthood between the second and fourth decades of life. This demographic profile overlaps substantially with that of primary migraine, and distinguishing the two requires attention to associated features of the syndrome rather than to headache characteristics alone. The associated burden on quality of life is substantial and often precedes the diagnosis of the syndrome by several years. Antiphospholipid antibodies induce endothelial activation in cerebral vessels, promoting vasoconstriction through mediators such as endothelin-1, and also alter platelet activation and serotonin metabolism, processes linked to migraine pathogenesis independent of the syndrome. Reversible cerebral vasoconstriction syndrome has been reported in association with antiphospholipid syndrome and should be considered in patients presenting with thunderclap headache. Rarely, the headache reflects a central nervous system vasculitis phenotype with multifocal cerebral arterial stenosis, in which immune-directed treatment has been reported to improve the arterial stenosis.

Seizures occur in approximately 7 percent of patients with antiphospholipid syndrome, a frequency nearly 10 times that of the general population, and occur more frequently in patients with associated systemic lupus erythematosus than in those with primary disease. Cerebral thromboembolic events are the factor most strongly associated with seizures, with poststroke epilepsy reaching 17 percent in the syndrome, higher than the rate of approximately 10 percent in the general poststroke population. Yet seizures also occur without a demonstrable infarct, and conventional MRI is normal in 30 to 40 percent of patients. The mechanisms involve both microthrombosis and a direct immune-mediated effect on neurons. In experimental antiphospholipid syndrome, antibodies accumulate in inhibitory cortical and hippocampal neurons, and patient-derived antibodies reduce inhibitory GABA-A receptor signaling. Acute symptomatic seizures occur in 30 to 40 percent of patients with cerebral venous thrombosis, a higher proportion than in arterial stroke, providing an additional substrate for seizure activity.

To address the diagnostic gap, the review proposes a three-tier framework for the layered evaluation and clinical attribution of these neurological manifestations. The first tier is clinical recognition and high-resolution phenotyping, beginning with a low threshold for suspicion and a comprehensive antiphospholipid antibody profile, including non-criteria antibodies where available, obtained early rather than after other causes are exhausted. The second tier selects imaging by symptom. Diffusion tensor imaging can detect microstructural white-matter injury when conventional MRI is unremarkable in cognitive dysfunction, and single-photon emission computed tomography reveals perfusion defects that correlate with cognitive impairment. In chorea, positron emission tomography shows striatal hypermetabolism indicating active dysfunction rather than tissue loss. In migraine, magnetic resonance angiography and vessel-wall imaging are indicated when reversible cerebral vasoconstriction syndrome is suspected. In seizures, structural imaging adds little, so evaluation depends on phenotyping and mechanistic markers. The third tier links these findings to mechanism, using serum neurofilament light chain and glial fibrillary acidic protein to quantify neuronal and astrocytic injury, though their value outside systemic lupus erythematosus remains undefined. Non-criteria antibodies improve sensitivity in seronegative cases and refine risk stratification, while markers of complement activation may identify candidates for complement-directed therapy.

The threshold for moving beyond the first tier should fall in patients with high-risk antibody profiles or concurrent systemic lupus erythematosus, since triple positivity carries the strongest association with thrombotic and overall disease burden. In these patients, advanced imaging and mechanistic biomarkers warrant earlier use rather than reservation for refractory cases. Three areas remain open for future study: the thrombo-inflammatory axis involving complement activation, neutrophil extracellular traps, and platelet activation; antibody-mediated central nervous system injury, where the binding of antibodies to neuronal and glial targets needs characterization specifically in the syndrome; and the boundary between antiphospholipid syndrome and systemic lupus erythematosus, whose shared and distinct central nervous system features remain incompletely defined. Recognizing antiphospholipid syndrome as a neurovascular-immune dysfunction, rather than purely a thrombotic disorder, may improve diagnosis and care for patients whose neurological symptoms remain unexplained by conventional investigation.

Subject of Research: Non-thrombotic neurological manifestations of antiphospholipid syndrome

Article Title: The brain in antiphospholipid syndrome beyond thrombosis

Article References: Fujieda, Y. (2026). The brain in antiphospholipid syndrome beyond thrombosis. Frontiers in Lupus, 4, Article 1908878. https://doi.org/10.3389/flupu.2026.1908878

Image Credits: AI Generated

DOI: 10.3389/flupu.2026.1908878

Keywords: brain, antiphospholipid, syndrome, beyond, thrombosis, scientific research