Diagnostics for AFM include brain and spinal cord MRI, nasopharyngeal swab collection for enteroviral PCR tests, CSF studies, and serum antibody testing for anti-MOG antibody and anti-AQP4 antibody (CDC, 2023). It is important that the tests are done as soon as possible after the patient develops symptoms.
Criteria for a probable case of AFM requires (CDC, 2023):
- Acute onset of focal limb weakness
- Cerebrospinal fluid pleocytosis with mild to moderate elevation in white blood cell count (<100 per μL with lymphocytic predominance)
Clinical criteria for a confirmed case of AFM requires (CDC, 2023; Murphy et al., 2021):
- Acute onset of flaccid limb weakness
- A spinal cord lesion on MRI is largely restricted to gray matter and spans one or more spinal segments. This is demonstrated by hyperintensity of the spinal cord grey matter. This is the hallmark of AFM
The following information includes CDC requested confirmatory testing (CDC, 2023):
Case reporting, for public health tracking purposes, follows the CDC case definition of presenting illness with onset of acute flaccid limb weakness. Confirmatory evidence of MRI with spinal cord lesion largely restricted to gray matter, while supportive evidence requires a CSF with pleocytosis (Greenberg, 2022).
The CDC also requests that healthcare professionals collect and submit specimens to the CDC for testing as early as possible in the illness. These requested specimens include cerebrospinal fluid, blood, and stool (CDC, 2023). The CDC requests submission of nasal (mid-turbinate) or nasopharyngeal plus oropharyngeal swab specimens only if the patient tests positive for enterovirus or rhinovirus at an external lab (CDC, 2023). Specimens that are submitted to the CDC are not intended for clinical diagnosis. Pathogen-specific testing should be performed at a hospital or state public health laboratories (CDC, 2023).