Notes from the Field: Six Cases of Acute Flaccid Myelitis in Children — Minnesota, 2018

During September 14–October 1, 2018, the Minnesota Department of Health (MDH) was notified of six children hospitalized in the Minneapolis-St. Paul region with symptoms consistent with acute flaccid myelitis (AFM). A confirmed case of AFM is defined as acute onset of flaccid limb weakness with magnetic resonance image indicating spinal cord lesions largely restricted to gray matter and spanning one or more vertebral segments (1). All six cases were confirmed by CDC. After a cluster of three cases occurred in 2014, an average of fewer than one AFM case per year had been reported to MDH. Among the six patients, the median patient age was 6.0 years (range = 1.3–9.2 years). All children resided in different Minnesota counties, and all experienced fever and upper respiratory signs and symptoms (e.g., rhinorrhea and cough) beginning a median of 8 days (range = 5–11 days) before weakness onset; none had a history of being immunocompromised. In addition, four patients experienced neck pain or headache, and two experienced diarrhea before weakness onset. Four patients had marked weakness of proximal muscle groups in one arm, although distal motor function was largely preserved. The other two patients initially had weakness in one leg, which became bilateral and rapidly ascended during hospitalization; both of these patients required endotracheal intubation and mechanical ventilation. In all six patients, limb weakness was first noted after waking in the morning. No epidemiologic links among patients were identified. All six patients were hospitalized. Three patients were discharged home, and two were discharged to inpatient rehabilitation facilities. One patient remains hospitalized with complete paralysis of all voluntary muscles, including the diaphragm, at the time of this report. All discharged patients had residual weakness at time of discharge; among these patients, the median duration of hospitalization was 8 days (range = 1–14 days). Magnetic resonance imaging (MRI) indicated spinal cord gray matter involvement in all six patients, largely in the anterior horns. The extent of gray matter involvement did not always correlate with deficits seen on physical exam; in three patients with only single limb weakness, multisegment gray matter involvement was apparent. Among all patients, three had anterior nerve root and facial nerve enhancement, and two had basilar and brainstem involvement. Three patients had normal MRI findings early in the illness course, but demonstrated extensive gray matter involvement on a subsequent MRI. Cerebrospinal fluid (CSF) was collected in five patients, with pleocytosis (white blood cell count >5 cells/mm3) present in two patients (Table). One CSF specimen (patient B) was positive for enterovirus (not typed) by reverse transcription–polymerase chain reaction (RT-PCR) at a commercial reference laboratory. Serum, CSF, stool, and nasopharyngeal specimens from five patients were tested at CDC. One nasopharyngeal swab (patient D) was positive for enterovirus-D68 (EV-D68) by real-time RT-PCR. One nasal wash specimen from patient B was positive for EV-D68 and a second specimen for EV-D68 and parechovirus A6 by real-time RT-PCR; CSF from this patient also was positive for EV-D68. The remaining specimens were negative, including those from three patients who had no positive specimens. All stool specimens were negative for poliovirus. Five of six patients received some form of immunomodulatory treatment (Table). One patient was treated with steroids and plasmapheresis followed by intravenous immune globulin (IVIG), one with steroids followed by IVIG, three with only IVIG, and one with supportive care only. This AFM cluster, the largest identified in Minnesota, occurred during a period of increased reporting of AFM nationally and is consistent with the epidemiologic and clinical characteristics of previously described AFM clusters (2–6). Despite report of upper respiratory tract signs and symptoms in all patients, testing for viruses that commonly cause upper respiratory tract infections was positive from nonsterile specimens in only two cases. EV-D68 in the CSF of patient B is considered the cause of AFM in this patient. Detection of a pathogen in the CSF might be related to the severity and prolonged nature of illness in this patient; however, host or other factors contributing to illness severity are unknown. AFM is a rare but serious cause of sudden onset limb weakness, especially in children, and should be considered in the differential diagnosis. Diagnosis and care of patients with AFM includes early collection of specimens, including CSF, for laboratory testing, MRI scans, and consultation with neurology and infectious disease experts. Potential cases should be reported to public health departments in a timely manner. Public health classification of AFM cases involves expert review of clinical and imaging findings; however, it is important that clinical care not be delayed pending case classification.

During September 14-October 1, 2018, the Minnesota Department of Health (MDH) was notified of six children hospitalized in the Minneapolis-St. Paul region with symptoms consistent with acute flaccid myelitis (AFM). A confirmed case of AFM is defined as acute onset of flaccid limb weakness with magnetic resonance image indicating spinal cord lesions largely restricted to gray matter and spanning one or more vertebral segments (1). All six cases were confirmed by CDC. After a cluster of three cases occurred in 2014, an average of fewer than one AFM case per year had been reported to MDH.
Among the six patients, the median patient age was 6.0 years (range = 1.3-9.2 years). All children resided in different Minnesota counties, and all experienced fever and upper respiratory signs and symptoms (e.g., rhinorrhea and cough) beginning a median of 8 days (range = 5-11 days) before weakness onset; none had a history of being immunocompromised. In addition, four patients experienced neck pain or headache, and two experienced diarrhea before weakness onset. Four patients had marked weakness of proximal muscle groups in one arm, although distal motor function was largely preserved. The other two patients initially had weakness in one leg, which became bilateral and rapidly ascended during hospitalization; both of these patients required endotracheal intubation and mechanical ventilation. In all six patients, limb weakness was first noted after waking in the morning. No epidemiologic links among patients were identified.
All six patients were hospitalized. Three patients were discharged home, and two were discharged to inpatient rehabilitation facilities. One patient remains hospitalized with complete paralysis of all voluntary muscles, including the diaphragm, at the time of this report. All discharged patients had residual weakness at time of discharge; among these patients, the median duration of hospitalization was 8 days (range = 1-14 days).
Magnetic resonance imaging (MRI) indicated spinal cord gray matter involvement in all six patients, largely in the anterior horns. The extent of gray matter involvement did not always correlate with deficits seen on physical exam; in three patients with only single limb weakness, multisegment gray matter involvement was apparent. Among all patients, three had anterior nerve root and facial nerve enhancement, and two had basilar and brainstem involvement. Three patients had normal MRI findings early in the illness course, but demonstrated extensive gray matter involvement on a subsequent MRI.
Cerebrospinal fluid (CSF) was collected in five patients, with pleocytosis (white blood cell count >5 cells/mm 3 ) present in two patients (Table). One CSF specimen (patient B) was positive for enterovirus (not typed) by reverse transcription-polymerase chain reaction (RT-PCR) at a commercial reference laboratory. Serum, CSF, stool, and nasopharyngeal specimens from five patients were tested at CDC. One nasopharyngeal swab (patient D) was positive for enterovirus-D68 (EV-D68) by real-time RT-PCR. One nasal wash specimen from patient B was positive for EV-D68 and a second specimen for EV-D68 and parechovirus A6 by real-time RT-PCR; CSF from this patient also was positive for EV-D68. The remaining specimens were negative, including those from three patients who had no positive specimens. All stool specimens were negative for poliovirus.
Five of six patients received some form of immunomodulatory treatment (Table). One patient was treated with steroids and plasmapheresis followed by intravenous immune globulin (IVIG), one with steroids followed by IVIG, three with only IVIG, and one with supportive care only.
This AFM cluster, the largest identified in Minnesota, occurred during a period of increased reporting of AFM nationally and is consistent with the epidemiologic and clinical characteristics of previously described AFM clusters (2)(3)(4)(5)(6). Despite report of upper respiratory tract signs and symptoms in all patients, testing for viruses that commonly cause upper respiratory tract infections was positive from nonsterile specimens in only two cases. EV-D68 in the CSF of patient B is considered the cause of AFM in this patient. Detection of a pathogen in the CSF might be related to the severity and prolonged nature of illness in this patient; however, host or other factors contributing to illness severity are unknown.
AFM is a rare but serious cause of sudden onset limb weakness, especially in children, and should be considered in the differential diagnosis. Diagnosis and care of patients with AFM includes early collection of specimens, including CSF, for laboratory testing, MRI scans, and consultation with neurology and infectious disease experts. Potential cases should be reported to public health departments in a timely manner. Public health classification of AFM cases involves expert review of clinical and imaging findings; however, it is important that clinical care not be delayed pending case classification.