Posterior reversible encephalopathy syndrome is present in a small minority of patients.This condition features the unique property that the patients cerebral arteries can spontaneously constrict and relax back and forth over a period of time without intervention and without clinical findings. Vasospasm is common post subarachnoid hemorrhage and cerebral aneurysm, but in RCVS only 25% of patients have symptoms post subarachnoid hemorrhage. Causes
The direct cause of the symptoms is believed to be either constriction or dilation of blood vessels in the brain. The pathogenesis is not known definitively, and the condition is likely to result from multiple different disease processes.Up to two-thirds of RCVS cases are associated with an underlying condition or exposure, particularly vasoactive or recreational drug use, complications of pregnancy (eclampsia and pre-eclampsia), and the adjustment period following childbirth called puerperium. Vasoactive drug use is found in about 50% of cases. Implicated drugs include selective serotonin reuptake inhibitors, weight-loss pills such as Hydroxycut, alpha-sympathomimetic decongestants, acute migraine medications, pseudoephedrine, epinephrine, cocaine, and cannabis, among many others. It sometimes follows blood transfusions, certain surgical procedures, swimming, bathing, high altitude experiences, sexual activity, exercise, or coughing. Symptoms can take days or a few months to manifest after a trigger.Following a study and publication in 2007, it is also thought SSRIs, uncontrolled hypertension, endocrine abnormality, and neurosurgical trauma are indicated to potentially cause vasospasm. Diagnosis
The clinician should first rule out conditions with similar symptoms, such as subarachnoid hemorrhage, ischemic stroke, pituitary apoplexy, cerebral artery dissection, meningitis, and  spontaneous cerebrospinal fluid leak.
This may involve a CT scan, lumbar puncture, MRI, and other tests. Posterior reversible encephalopathy syndrome has a similar presentation, and is found in 10–38% of RCVS patients.RCVS is diagnosed by detecting diffuse reversible cerebral vasoconstriction. Catheter angiography is ideal, but computed tomography angiography and magnetic resonance angiography can identify about 70% of cases. Multiple angiographies may be necessary. Because other diseases (such as atherosclerosis) have similar angiographic presentations, it can only be conclusively diagnosed if vasoconstriction resolves within 12 weeks. Treatment
As of 2014, no treatment strategy has yet been investigated in a randomized clinical trial. Verapamil, nimodipine, and other calcium channel blockers may help reduce the intensity and frequency of the headaches. A clinician may recommend rest and the avoidance of activities or vasoactive drugs which trigger symptoms (see § Causes). Analgesics and anticonvulsants can help manage pain and seizures, respectively. Prognosis
All symptoms normally resolve within three weeks, and may only last days. Permanent deficits are seen in a minority of patients, ranging from under 10% to 20% in various studies. Less than 5% of patients experience progressive vasoconstriction, which can lead to stroke, progressive cerebral edema, or even death. Severe complications appear to be more common in postpartum mothers. Epidemiology
The incidence of RCVS is unknown, but it is believed to be "not uncommon", and likely under-diagnosed.