Nothing is more concerning to parents and emergency health care providers than a serious illness that primarily impacts children. The concern is heightened when we don’t know the cause of the illness. These are the current circumstances for acute flaccid myelitis (AFM), and there is currently an ongoing seasonal outbreak of the disease in the United States.

AFM is a rare condition that, similar to polio, destroys gray matter in the spinal cord, resulting in weakness that can progress to flaccid paralysis in hours. The condition first attracted attention in the United States in 2014 during a seasonal enterovirus outbreak.^1-4 The Centers for Disease Control and Prevention (CDC) has raised concern because AFM cases have continued to show seasonal peaks each year since 2014 (see Figure 1), and we still don’t know the cause.^5-7 In addition, AFM is being discussed in the news, generating increased awareness and apprehension. Clinicians are being encouraged to enhance their knowledge about AFM and rapidly engage departments of health for information on appropriate diagnostic and sampling methods for suspected cases.

The Background on AFM

Since it was first identified in 2014, there have been approximately 386 confirmed cases of AFM.^5-7 The disorder is extremely rare, literally about one in a million. The mean age of patients is 4 years, with 90 percent of all cases occurring in patients younger than 18 years old. Despite research, we still don’t know the cause.⁵ Initially, all signs pointed to an enterovirus type D68, but that theory has not panned out.^8,9 Continued investigations of possible sources including viruses, bacteria, and toxins, as well as inflammatory, autoimmune, and genetic disorders have all failed to clearly identify a culprit.

Prognosis

Little information exists regarding long-term prognosis of AFM. A general review of the existing reports suggests that out of 138 cases followed between 30 days to six months, 89.8 percent had persistent neurologic deficits, 8.7 percent were fully recovered, and 1.5 percent resulted in death.^4,7,9,10

Clinical Presentation and Diagnosis

AFM should be suspected when patients (usually young) present with extremity weakness that is rapidly progressing. Early studies suggested up to 80 percent of patients reported an antecedent upper respiratory infection or enteritis.^2,11 Another report noted that 75 percent of the cases had a low-grade fever a few days prior to onset of weakness.^12,13 However, neither of these findings are consistent.^1,4,7 Some patients present with an initial tingling and/or pain in the extremities. Urinary retention or a neurogenic bladder has been noted in some. Respiratory failure requiring mechanical ventilation may develop rapidly. Additional presentations include facial palsy, ptosis, extraocular paresis, altered mental status, and bulbar findings such as slurred speech and dysphagia.^10,13