Acute flaccid myelitis is diagnosed based upon clinical exam, magnetic resonance imaging (MRI) of the spinal cord, and analysis of cerebrospinal fluid (CSF) (usually with increased white blood cells or pleocytosis). On MRI of the spinal cord, AFM lesions are longitudinal throughout the grey matter (the anterior horn cells). Sometimes imaging may appear normal early in the disease, but repeat imaging shows the lesions. In some situations, electrophysiological studies of the nerves and muscle (called nerve conduction and electromyogram [NCS/EMG]) may help to determine if there is injury to the lower motor neuron. Testing may also include blood draws, respiratory tract samples, or collection of other bodily fluids to determine if a viral or infectious cause is present.