Both perilesional edema and seizures are common in patients with neurocysticercosis, and according to a study in the December 2008 Lancet Neurology, half of patients with calcified neurocysticercosis who had seizures demonstrated perilesional edema on MRI. The findings “suggest a unique and possibly preventable cause of seizures in this population,” said Theodore Nash, MD, Head of the Gastrointestinal Parasites Section of the Laboratory of Parasitic Diseases at the National Institute of Allergy and Infectious Diseases, NIH, in Bethesda, Maryland, and colleagues.
Neurocysticercosis is caused by infection of the tapeworm Taenia solium. Calcified lesions are the most common cerebral finding in patients with neurocysticercosis, occurring in 10% to 20% of patients in endemic regions. “Increasing evidence implicated calcified neurocysticercosis in the development and maintenance of seizures and epilepsy,” noted Dr. Nash and colleagues. Perilesional edema around the calcified cysts, as seen on CT or MRI, has been mistaken for refractory neurocysticercosis, leading to unnecessary anthelmintic therapy or brain biopsy.
The researchers identified 110 neurocysticercosis patients (ages 17 to 65) in Lima, Peru, who had calcified lesions and a history of seizures (n = 106) or severe headaches (n = 4). Excluded were patients with a history of status epilepticus, focal MRI findings (viable cysts on MRI, baseline perilesional edema, or brain lesions not due to neurocysticercosis), or other potentially confounding factors. MRI was performed at baseline and within five days of a seizure to assess the presence of perilesional edema, defined as transient T2 or fluid-attenuated inversion recovery (FLAIR) signals in the region of calcified lesions and were at least twice the size of the implicated calcified focus. Unchanging FLAIR signals in the region of a calcification were considered chronic gliosis, not perilesional edema. Patients were followed from November 1999 through 2006.
Findings showed that 29 (26%) of the 110 subjects had a new incident seizure; of these, 28 had a history of seizures. The estimated five-year incidence of seizure relapses was 36%. Twenty-four patients with relapse had an MRI within five days of the event; 50% of this group had perilesional edema, compared with 9% of 23 asymptomatic, matched controls. Subjects who had seizures were more likely to be taking antiepileptic drugs and to have a history of seizures.
“In order to assess the extent of inflammation and microglial activity in the region of the calcified lesion with perilesional edema, we are currently studying patients with PET scans, using peripheral benzodiazepine receptor ligands,” Dr. Nash concluded.
—Andrew N. Wilner, MD