Question

Where is the typical location of an axillary nerve lesion, and what features may be observed?

A) Proximal with motor weakness
B) Distal with sensory loss
C) Midway with tingling sensations
D) Superficial with muscle spasms

Answer 1

An axillary nerve lesion typically occurs proximally, often resulting in motor weakness of the arm due to impairment of the deltoid muscle. Sensory loss over the lateral aspect of the shoulder may also be present due to the sensory innervation of the axillary nerve.

Step-by-step explanation:

The typical location of an axillary nerve lesion is proximal, and it may exhibit features of motor weakness (Option A). This is because the axillary nerve, which originates from the posterior cord of the brachial plexus and supplies the deltoid and teres minor muscles, as well as sensory input to the skin covering part of the deltoid, is susceptible to injury near the surgical neck of the humerus or as a result of a dislocated shoulder. A lesion here would affect the motor function, leading to weakness in arm abduction beyond 15 degrees, as the deltoid muscle is primarily responsible for this action. Additionally, due to the sensory innervation of the axillary nerve to the skin covering the deltoid, sensory loss can be observed over the lateral aspect of the shoulder. However, flaccid paralysis and decreased or lost reflexes are more indicative of a lower motor neuron (LMN) lesion, as opposed to the spasticity observed in upper motor neuron (UMN) lesions.