Lyme disease is caused by the parasite Borrelia burgdorferi, which is carried by ticks. Humans develop Lyme disease after receiving a bite from an infected tick. Early diagnosis and treatment with antibiotics usually cures the disease and removes all symptoms. However, if the disease is not treated, it can spread to other parts of the body, including the spleen, and cause additional symptoms.
If the parasite that causes Lyme disease is not treated, if can spread to other parts of the body. Some patients with untreated Lyme disease may develop an enlarged spleen, according to the North Caroline Lyme Disease Foundation. The spleen is a small, fist-sized organ that is found underneath the ribcage, on the left side of the body. The spleen filters blood and produces white blood cells used by the immune system to fight disease. Certain types of infection, such as Lyme disease, can cause the spleen to swell.
If the spleen becomes enlarged, it can cause several additional symptoms. The most common is pain or tenderness in the area of the spleen, on the left side of the back just under the rib cage. The pain may sometimes spread to the left shoulder. If the spleen presses on the stomach, it can causes feelings of fullness after eating only a small amount of food, or without eating anything, explains the Mayo Clinic. Doctors can usually diagnose an enlarged spleen through a physical examination.
Because the spleen filters blood and regulates the blood supply, an enlarged spleen can cause anemia, or low levels of red blood cells in the blood. An enlarged spleen tends to hold onto more red blood cells than it needs to, instead of releasing them into the bloodstream. If red blood cells levels drop too low, additional symptoms may result, such as easy bleeding and trouble clotting, according to the Merck Manuals. People with an enlarged spleen may also suffer from fatigue and feelings of weakness and tiredness.