Effectiveness of Ultrasound-Guided Hydrodissection for Atypical Anterior Cutaneous Nerve Entrapment Syndrome Presenting as Lower Back Pain Due to Retrograde Neuropathic Pain

This case report describes an atypical presentation of anterior cutaneous nerve entrapment syndrome (ACNES). A male patient with refractory lower back pain without typical abdominal symptoms exhibited localized tenderness in the abdominal wall. The patient's back pain was reproduced by compression of the tender point. Color Doppler ultrasonography revealed a pulsating perforating artery directly beneath the tender point. Ultrasound-guided hydrodissection was performed at the site, resulting in resolution of Carnett's sign and significant improvement in both pain and motor function. This case suggests that retrograde neuropathic pain (RNP) may arise from entrapment of the anterior cutaneous nerve, manifesting as referred pain in the lower back. Even in the absence of abdominal symptoms, a positive Carnett's sign should prompt the consideration of abdominal wall nerve entrapment and associated RNP in the differential diagnosis of refractory low back pain.