69 year old female with recently diagnosed acute myeloid leukemia undergoing induction chemotherapy for which neurology was consulted for progression right foot drop. Symptoms began as mild gait difficulty with decreased foot clearance on right which progressed to frank foot drop. On exam she had dorsiflexion weakness with disproportionate weakness in extension of the hallux and minimal plantar flexion weakness. There was  sensory loss isolated to the interdigital space between the hallux and second digit of the affected foot with symmetric reflexes and without radicular signs.

Initial diagnostic concern was for deep peroneal neuropathy for which MRI of the right lower extremity revealed 1) diffuse edema involving muscles at the anterior compartment of the leg, proximal peroneus longus muscle, and medial/lateral gastrocnemius, and 2) an intramedullary lesion was also detected at the posterolateral aspect at the proximal tibia and proximal fibular diaphysis.

The infiltration of AML into skeletal muscles is a rare phenomenon, and its atypical presentation as foot drop is even more uncommon. It underscores the necessity of considering malignancy as a potential cause of suspected compressive neuropathies, especially when standard etiologies have been ruled out.