Bilateral Globus Pallidus Lesions and Delayed Hypoxic Encephalopathy Induced by Overuse of Transdermal Fentanyl Patches.

We describe a rare case of bilateral globus pallidus lesions (BPL) and delayed hypoxic encephalopathy (DHE) induced by the overuse of transdermal fentanyl patches. The patient was a 54-year-old woman, who had a history of unexplained, intractable anal pain, for which several medications were prescribed, but with very limited effectiveness. Four days prior to admission, she was newly prescribed transdermal fentanyl patches at a dose of 4 mg/day. She developed impaired consciousness and respiratory distress after applying more than 10 fentanyl patches across her body. Brain computed tomography (CT) revealed a lesion in the left globus pallidus. She was treated with naloxone and mechanical ventilation in the intensive care unit and regained consciousness, being discharged from the hospital on day 9. However, she later experienced cognitive and behavioral changes, prompting a return to her previous hospital. Brain magnetic resonance imaging (MRI) revealed BPL with hyperintensities on T2-weighted imaging. After readmission, she again developed impaired consciousness and became fully dependent on care. Although her consciousness gradually improved, she developed higher brain dysfunction, myoclonus, and parkinsonism. A follow-up brain MRI two months after the initial onset showed abnormal signals in the deep white matter bilaterally, along with BPL, with hyperintensities in limited areas on T1-weighted imaging and widespread hyperintensities on T2-weighted imaging. The diagnosis of DHE was based on the extent of bilateral white matter lesions. With rehabilitation treatment, her condition improved to the point where she could manage daily life, though attention and memory impairments persisted. Transdermal fentanyl patches are widely used in clinical practice due to their high efficacy and safety. However, fentanyl overuse has been associated with BPL and DHE, although the exact mechanism remains unclear. This report highlights that even with transdermal administration, overdose can lead to severe neurological side effects.