Peripheral Nerve Microscopic Changes Related to Study Procedures: Two Nonclinical Case Studies

Peripheral nerves are routinely examined microscopically during the nonclinical safety assessment of therapeutics. In addition to test article-related on- or off-target changes, microscopic changes in peripheral nerves may also be caused by study procedures, such as parenteral test article administration and blood or tissue sampling. We present 2 nonclinical case studies in which nonstandard peripheral nerves had study procedure-related histologic changes. The first case study describes mouse trigeminal nerve changes as a result of blood sampling via retro-orbital sinus puncture. These changes included minimal-to-mild nerve fiber (axonal) degeneration associated with macrophage infiltration. The second case study presents rat brachial plexus changes associated with animal handling and blood sampling. Brachial plexus changes included minimal-to-moderate inflammation, focal hemorrhage, and nerve fiber degeneration. In both cases, the histological changes were morphologically indistinguishable from those that might be due to test article. Therefore, careful consideration of the incidence and severity across groups and a review of study procedures to rule out handling-related nerve damage are essential before identifying a test article-related effect on peripheral nerves. Study design considerations to avoid such procedure-related changes will be discussed, as well as sampling strategies to help distinguish these from test article-related effects.