Arm Paralysis After Routine Childhood Vaccinations: Application of Advanced Molecular Methods to the Causality Assessment of an Adverse Event After Immunization.

Post-licensure surveillance for adverse events following immunizations (AEFI) can identify rare complications of vaccinations and rigorous vaccine adverse event causality assessments can help to identify possible causal relationships. We report the development of arm paralysis after varicella vaccination in a 1-year-old child. Paralysis was initially presumed to be due to vOka because of the temporal relationship between vaccination and onset of arm weakness; however, molecular studies identified wild-type varicella zoster virus VZV (WT-VZV) in the CSF, leading the authors to conclude that WT-VZV was the probable cause. This case illustrates the complexity of assessing AEFI causality, and the importance of careful and complete evaluations when determining the most likely cause of an AEFI.

Motor unit number estimation in the evaluation of focal conduction block.

Temporal dispersion and phase cancellation limit the utility of amplitude reduction in compound muscle action potential (CMAP) as a measure of focal conduction block but may not affect motor unit number estimation (MUNE). Hence, MUNE offers the potential of a specific measure of conduction block. We investigated the role of MUNE in 11 patients with ulnar neuropathy and conduction block at the elbow and also in 8 normal subjects. MUNE failed to detect motor unit dropout in the patient group because reduced values for surface-recorded motor unit potentials (SMUPs) were obtained at proximal locations, suggesting that focal compression selectively damages larger motor axons, an hypothesis that has support from animal studies. We conclude that, because MUNE is affected by the physiological characteristics of functional axons surviving the underlying pathological process, the utility of MUNE is limited to diseases in which the expected pathology affects motor axons uniformly.