A 37-year-old previously healthy man comes to the office for evaluation of enlarged lymph nodes. He has an 8-week history of progressively enlarging cervical lymph nodes associated with subjective fevers, fatigue, and drenching night sweats. After initial assessment, the patient undergoes excisional biopsy of enlarged lymph nodes in the left posterior triangle of the neck. Two weeks later, during a follow-up visit, he describes difficulty with overhead activities such as combing his hair or placing dishes on overhead shelves. Examination shows a left shoulder droop with weakness of left arm abduction above 100 degrees. Other shoulder movements are normal, and there is no sensory loss. Which of the following muscles is most likely paralyzed in this patient?

Question

A 37-year-old previously healthy man comes to the office for evaluation of enlarged lymph nodes.  He has an 8-week history of progressively enlarging cervical lymph nodes associated with subjective fevers, fatigue, and drenching night sweats.  After initial assessment, the patient undergoes excisional biopsy of enlarged lymph nodes in the left posterior triangle of the neck.  Two weeks later, during a follow-up visit, he describes difficulty with overhead activities such as combing his hair or placing dishes on overhead shelves.  Examination shows a left shoulder droop with weakness of left arm abduction above 100 degrees.  Other shoulder movements are normal, and there is no sensory loss.  Which of the following muscles is most likely paralyzed in this patient?

Quizplus · Accepted Answer

11ec160b_35a8_0daa_9249_2d426c628565_MD0001_00 The spinal accessory nerve (CN XI) is a pure motor nerve that innervates the sternocleidomastoid and trapezius. It follows a superficial course through the posterior triangle of the neck and is vulnerable to penetrating trauma and iatrogenic injury (eg, cervical lymph node dissection). The trapezius elevates and rotates the scapula upward (eg, during arm abduction) and stabilizes the shoulder. Symptoms of trapezius weakness include drooping of the shoulder, impaired abduction of the arm above 100 degrees, and lateral displacement of the scapula. If the injury involves the proximal portions of the nerve, weakness of the sternocleidomastoid may also occur. (Choice A) The deltoid is innervated by the axillary nerve (C5-6). Injury would cause impaired sensation over the lateral shoulder and weakness in abduction of the arm from 30 to 100 degrees. Iatrogenic axillary nerve injury can occur during shoulder surgery (eg, proximal humerus fracture repair) or intramuscular injection in the deltoid. (Choice B) The latissimus dorsi is innervated by the thoracodorsal nerve which can be damaged during axillary lymph node dissection. It is the most powerful adductor of the arm and assists with extension and medial rotation. (Choice C) The levator scapulae is innervated by the C3 and C4 cervical nerves and the dorsal scapular nerve (C5). It acts to elevate the scapula and rotate its medial border inferiorly but does not have a significant effect on arm abduction. (Choice D) The serratus anterior is innervated by the long thoracic nerve and protracts and rotates the scapula upward, assisting with elevation of the arm over the head. Although weakness of the serratus anterior causes winging of the scapula, it usually occurs following axillary lymph node dissection and would not be associated with shoulder droop. Educational objective: The spinal accessory nerve is vulnerable to injury in the posterior triangle of the neck. Injury results in weakness of the trapezius muscle, which presents with drooping of the shoulder, impaired abduction of the arm above 100 degrees, and lateral displacement of the scapula. __________ References: Spinal accessory nerve injury: eight cases and review of the literature. (http://www.ncbi.nlm.nih.gov/pubmed/25203336)

A 37-Year-Old Previously Healthy Man Comes to the Office for Evaluation