The Phoenix Sign: Lidocaine Peripheral Nerve Block Improves Motor Strength and Macrovascular Flow in Diabetic Patients with Suspected Common Peroneal Nerve Entrapment — A Double-Blinded Pilot Study
Summary: In this small double-blinded randomized pilot study, four patients with diabetic peripheral neuropathy underwent bilateral peripheral nerve blocks with either lidocaine or papaverine. All patients demonstrated increased extensor hallucis longus (EHL) motor strength after injection (the Phoenix Sign). Lidocaine produced a statistically significant 151.7% increase in dorsalis pedis artery blood flow velocity (p=0.03). The findings support the Phoenix Sign as a potential diagnostic tool for Common Peroneal (Fibular) nerve entrapment and suggest a vasodilatory mechanism contributing to the rapid motor improvement observed.
Key Highlights:
- All patients showed increased EHL motor strength after injection (Phoenix Sign confirmed)
- Lidocaine produced a 151.7% increase in dorsalis pedis artery flow velocity (p=0.03)
- Posterior tibial artery flow also improved with lidocaine (37.4%, p=0.06)
- No detectable changes in microvascular perfusion via near-infrared spectroscopy
- Results support lidocaine nerve block as both a diagnostic test and potential therapeutic window for CPN entrapment in diabetic patients
Keywords: Phoenix Sign, common peroneal nerve entrapment, diabetic neuropathy nerve block, lidocaine DFU