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A young woman was diagnosed with acute disseminated encephalomyelitis (ADEM) after being vaccinated against SARS-CoV-2, neurologists in Europe said.

The case report involved a 19-year-old woman admitted to the hospital 2 weeks after receiving her first dose of the Moderna mRNA SARS-CoV-2 vaccine, reported Karolina Kania, MD, of Poznan University of Medical Sciences in Poland, and co-authors, in .

The patient was admitted with headache, fever, back pain, nausea, vomiting, and urinary retention. Brain and spinal cord MRI was distinctive for ADEM with widespread demyelinating lesions, and the patient was treated successfully with methylprednisolone.

ADEM involves a brief, widespread attack of that damages myelin. Long-term prognosis generally is favorable and most ADEM patients have total or near total recoveries, but others may have mild to moderate lifelong impairment including cognitive difficulties, weakness, loss of vision, or numbness.

ADEM can occur after viral or bacterial infections and has been reported after vaccination for measles, mumps, or rubella. It also has been reported in people with .

"Its pathogenesis is incompletely understood, but acute disseminated encephalomyelitis is a presumably autoimmune disorder that occurs rarely in children and adults," noted Lyell Jones, Jr., MD, of the Mayo Clinic in Rochester, Minnesota, who wasn't involved with the case.

"One population-based study found an overall incidence of ADEM in the range of 0.1 cases per 100,000 people per year," Jones told 乌鸦传媒. "Many patients with ADEM -- perhaps two or three out of four -- recall a recent infection, suggesting a parainfectious immune mechanism in some cases. Studies have not shown a reproducible association between the diagnosis of ADEM and recent antecedent immunization."

"Acute demyelinating events after vaccination are extremely rare, and causality is always very ," observed Robert Bermel, MD, of the Cleveland Clinic, who also wasn't involved with the case.

"The risk of neurological complications with COVID-19 disease is far, far higher than the risk of complications from the vaccines, which now have immense safety data to support their broad use," Bermel told 乌鸦传媒. "Neurological complications from COVID-19 disease can include stroke, encephalitis, myelitis, and those of us who have seen those complications in the hospital strongly urge all people to be vaccinated."

The patient was admitted with complaints of a 3-day severe headache, fever, back and neck pain, nausea, and vomiting 2 weeks after she received her first Moderna vaccine dose. She had noticed urinary retention the last 2 days. Exam was significant for nuchal rigidity and bilateral Babinski signs.

Brain MRI showed multiple, poorly demarcated, hyperintense lesions in both hemispheres. Cervical and thoracic MRI showed a widespread hyperintense area with overlapping lesions.

Cerebrospinal fluid (CSF) white blood cell (WBC) count was 294 × 10⁶/L (reference range, 0–5 × 10⁶/L). Protein levels were 648 mg/L (reference range, 200–400 mg/L). CSF was negative for antibodies to major pathogens and cultures of bacteria and fungi.

Oligoclonal bands in blood and CSF were negative. Blood tests for multiple antibodies, including aquaporin-4 and anti-myelin oligodendrocyte glycoprotein, were negative. The patient was treated empirically with ceftriaxone and acyclovir.

After ADEM was diagnosed, the patient was treated with methylprednisolone and her clinical status improved. Plasma exchange also was started but stopped due to allergic reaction.

Lumbar puncture was repeated 12 days after the first; CSF WBC count was 61 × 10⁶/L and protein levels were 338 mg/L. The patient was discharged without any symptoms except a mild headache, which persisted as her only symptom at 40-day follow-up.

"Our patient manifested a typical radiological pattern for ADEM with extensive, diffuse demyelinating lesions in the brain and along all cervical and thoracic spinal cord," Kania and colleagues wrote.

"The CSF examination results were specific for ADEM with pleocytosis and the absence of oligoclonal bands," the team added. "However, clinical urinary retention without lower limbs motor or sensory deficits is quite rare."

Two cases of ADEM have been reported in women who received the Sinovac inactivated SARS-CoV-2 vaccine (which is not used in the U.S.), Kania and co-authors noted. In Italy, a 56-year-old woman with a previous history of post-infectious rhombencephalitis was diagnosed with ADEM 2 weeks (Comirnaty) shot.

"It is easy for a casual reader to infer a causal relationship when, in fact, reports of this nature offer no insight into whether or not the COVID-19 vaccine alters the risk of ADEM or other neurological disorders," Jones said.

"Careful population-based or cohort studies, or analysis of large clinical trial outcomes, are needed to understand any relationship between COVID-19 vaccines and ADEM," Jones continued. "Case reports are useful to describe novel features of disease, but do not provide insights into risks or benefits at a population level."

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