A 20-year-old man is evaluated in the clinic for right arm weakness and numbness. He is a competitive baseball pitcher and says that he played a lot more innings than usual last week because his team made the playoffs. Since then, the patient has had difficulty using the right arm, particularly when lifting objects. He has no known history of head, neck, or upper extremity trauma. On physical examination, there is diminished strength on right elbow flexion and an absent biceps reflex. This patient is most likely to have sensory loss over which of the following areas?

Question

A 20-year-old man is evaluated in the clinic for right arm weakness and numbness.  He is a competitive baseball pitcher and says that he played a lot more innings than usual last week because his team made the playoffs.  Since then, the patient has had difficulty using the right arm, particularly when lifting objects.  He has no known history of head, neck, or upper extremity trauma.  On physical examination, there is diminished strength on right elbow flexion and an absent biceps reflex.  This patient is most likely to have sensory loss over which of the following areas?

Quizplus · Accepted Answer

11ec160b_3598_a438_9249_bf4121e51f37_MD0001_00 This patient likely has musculocutaneous nerve injury, which most commonly occurs in the setting of trauma (eg, shoulder dislocation) and strenuous upper extremity activity (eg, baseball pitching). The musculocutaneous nerve is derived from the C5-C7 spinal nerve roots and arises from the lateral cord of the brachial plexus. It innervates the major forearm flexors (eg, biceps brachii, brachialis) and coracobrachialis (flexes and adducts the arm). After innervating these muscles, the remaining fibers become the lateral cutaneous nerve of the forearm and provide sensory innervation to the skin of the lateral forearm. (Choice B) The medial forearm receives sensory innervation from a branch of the medial cord of the brachial plexus (medial cutaneous nerve of the forearm). (Choices C and D) The posterior arm and forearm receive sensory innervation from the posterior cutaneous branches of the radial nerve. (Choice E) The thenar eminence receives sensory innervation from the palmar cutaneous branch of the median nerve, which arises proximal to the carpal tunnel. Educational objective: The musculocutaneous nerve innervates the major forearm flexors (eg, biceps brachii, brachialis) and coracobrachialis (flexes and adducts the arm) and provides sensory innervation to the lateral forearm. It is derived from the upper trunk of the brachial plexus (C5-C7) and can be injured by trauma or strenuous upper extremity exercise. __________ References: Peripheral nerve entrapment and injury in the upper extremity. (http://www.ncbi.nlm.nih.gov/pubmed/20082510) Musculocutaneous neuropathy: case report and discussion. (http://www.ncbi.nlm.nih.gov/pubmed/20013159) Musculocutaneous nerve injury in major league baseball pitchers: a report of 2 cases. (http://www.ncbi.nlm.nih.gov/pubmed/17293466)

A 20-Year-Old Man Is Evaluated in the Clinic for Right