Point-of-Care Ultrasound in Japanese Mamushi ( <i>Gloydius blomhoffii</i> ) Bites: Presence of Deep Subcutaneous Hypoechoic Bands

Japanese mamushi (<i>Gloydius blomhoffii</i>) causes ∼3000 snakebites annually in Japan, but specific ultrasonographic findings have not been well characterized. Current severity assessment relies on visual grading systems based on local swelling and erythema, which may not provide sufficient information for timely and accurate treatment decisions. We present 3 pediatric patients (ages 7-9 y) with clinically diagnosed mamushi bites to the fingers, all presenting with Grade III envenomation (ie, swelling extending to the elbow). Point-of-care ultrasound examination revealed a remarkably consistent finding: a distinct hypoechoic band located in the deep subcutaneous layer immediately superficial to the muscle fascia. This characteristic band was most prominent at the bite site and gradually tapered off distally. Serial ultrasound examinations demonstrated progressive thinning and eventual disappearance of the hypoechoic band, correlating with clinical improvement following treatment with cepharanthine and anti-mamushi serum. Ultrasonography detected subcutaneous tissue changes beyond clinically apparent swelling in all cases, demonstrating superior sensitivity compared with visual assessment. All patients recovered without sequelae. These findings may differ from previously reported snakebite point-of-care ultrasound findings in terms of the anatomic location of the hypoechoic lesion. The hypoechoic bands observed in mamushi envenomation may serve as useful ultrasonographic markers for objective monitoring of treatment response and assisting with clinical management decisions, particularly regarding fasciotomy considerations and antivenom therapy guidance in the context of comprehensive clinical evaluation. These ultrasonographic features may not be species specific to mamushi but could represent common pathophysiologic responses to envenomation requiring validation across multiple species.