Usefulness of ultrasonography for diagnosing iatrogenic spinal accessory nerve palsy after lymph node needle biopsy: a case report

BACKGROUND: Spinal accessory nerve (SAN) palsy is rare in clinical settings. Iatrogenicity is the most common cause, with cervical lymph node biopsy accounting for > 50% of cases. However, SAN palsy after lymph node needle biopsy is extremely rare, and the injury site is difficult to identify because of the tiny needle mark. CASE PRESENTATION: A 26-year-old woman was referred to our hospital with left neck pain and difficulty abducting and shrugging her left shoulder after left cervical lymph node needle biopsy. Five weeks earlier, a needle biopsy had been performed at the surgery clinic because of suspected histiocytic necrotizing lymphadenitis. No trace of the needle biopsy site was found on the neck, but ultrasonography (US) showed SAN swelling within the posterior cervical triangle. At 3 months after the injury, her activities of daily living had not improved. Therefore, we decided to perform a surgical intervention after receiving informed consent. We performed neurolysis because the SAN was swollen in the area consistent with the US findings, and nerve continuity was preserved. Shoulder shrugging movement improved at 1 week postoperatively, and the trapezius muscle manual muscle testing score recovered to 5 at 1 year postoperatively. The swelling diameter on US gradually decreased from 1.8 mm preoperatively to 0.9 mm at 6 months. CONCLUSION: We experienced a rare case in which US was useful for iatrogenic SAN palsy. Our results suggest that preoperative US is useful for localization of SAN palsy and that postoperative US for morphological evaluation of the SAN can help assess recovery.