Final answer:
The probable cause for referred pain in the left shoulder for a patient with Mono is inflammation of the spleen, connected with Kehr's sign. This occurs because the brain misinterprets the pain originating from visceral sensory fibers connected to the spleen as coming from the left shoulder.
Step-by-step explanation:
Possible Cause of Referred Pain to the Left Shoulder in a Mono Patient
The most likely cause of referred pain to the left shoulder in a patient with a history of Infectious Mononucleosis (Mono) is inflammation of the spleen. This condition is related to Kehr's sign, which is associated with splenic rupture. The spleen is located in the upper-left quadrant of the abdomen, and pain can be felt more acutely in the shoulder due to the way in which certain visceral sensory fibers connected to the spleen interact with the nervous system. These fibers from the spleen enter the spinal cord at the same level as fibers from the shoulder, leading the brain to mistakenly interpret abdominal discomfort as shoulder pain.
Other options such as enlarged lymph nodes, irritation of the diaphragm, or liver infection may cause discomfort but are less likely to cause referred pain specifically in the left shoulder compared to spleen-related issues in the context of Mono. This is because the sensory pathways from these regions do not correspond as closely with the nerve levels associated with the left shoulder region as described by the mechanism of referred pain.