A retrospective, multicenter US study on acute disseminated encephalomyelitis (ADEM)

A recent study published on acute disseminated encephalomyelitis (ADEM) is the largest study on ADEM that has been conducted. This study was a retrospective multicenter study where the authors looked at data from the past and from several sites. The authors searched five hospitals for billing codes used for ADEM to get the data.

The study included 228 patients who were initially diagnosed with ADEM; 122 were children and 106 were adults. The authors looked to see whether the diagnosis of ADEM was based on diagnostic criteria from the 2007 International Pediatric Multiple Sclerosis Study Group (IPMSSG). For 70% of the pediatric patients and 47% of the adult patients, the diagnosis was based on the IPMSSG criteria. Many patients included in this retrospective study (spanning years from 1985 to 2014) would not have been diagnosed with ADEM according to current criteria.

More than half (61%) of the patients had an infection less than four weeks prior to the onset of ADEM. Ten (4%) patients had received a vaccination less than four weeks prior to their onset, and seven of them also had an infection in that time frame. Seasonal differences in onset were not seen. The most common presenting symptoms reported were headache, issues with walking, weakness, and fever.

Patients were followed for a median of two years. At the end of follow-up, most patients (68%) did not have another attack, and 32% were given a diagnosis other than monophasic ADEM, which included MS (11%), and NMOSD (4%). The authors identified multiphasic ADEM as a diagnosis in 22 patients (10%). Most (85%) of the patients who had another attack, had it within 2 years of onset.

In this retrospective study, the authors reported that 82% of the patients received steroids, and some received IVIg and/or plasmapheresis (PLEX). The article did not describe the effectiveness of these treatments but found that those who needed PLEX or IVIg had a significantly lower chance of having a favorable outcome. A favorable outcome was defined as a modified Rankin Scale score that was equal or less to 2.

The authors also looked at what factors predicted relapses. Females were more likely to have relapses. Patients without encephalopathy at onset were more likely than those with encephalopathy to have relapses (and would not have met strict ADEM criteria under current approaches). Pediatric patients who had relapses were more likely to be diagnosed with multiphasic ADEM than adults. This might be because physicians may not want to diagnose children with MS because it is a disease that requires treatments throughout life. Children were more likely to have a favorable outcome than adults.

This study indicates that follow-up after the onset of ADEM should happen for at least two years to monitor for recurrence. This is because most relapses occurred within two years. 10% of patients in this study who were monophasic for two years had a relapse after this time (some had a relapse 5-10 years after onset). This study is limited by the fact that patients were not followed consistently, patients who had a multiphasic disease were followed for a longer period of time than those with a monophasic disease. Also, because there is no biomarker for ADEM, this makes a proper diagnosis especially hard to get. The authors argue that the IPMSSG diagnostic criteria may be more useful for diagnosis in children than in adults. The authors also state that, “most patients with a relapsing disease after an initial ADEM diagnosis are probably representations of MS.”

Notably missing from this study was an analysis of outcomes other than relapse or modified Rankin Scale. Patients, especially pediatric patients, will require longer follow up to understand the potential cognitive impacts of ADEM. Also, this study did not include anti-Myelin Oligodendrocyte Glycoprotein (MOG) antibody testing, which may explain the percent of patients who relapsed. In general, ADEM (when strict criteria are applied) remains a one-time event. Prospective studies, or studies that follow patients starting at diagnosis and into the future, are needed.