Are mood swings a sign of lyme disease?

This would be a very, very unusual presentation of Lyme's disease. I would say that without other symptoms this is NOT LYME'S DISEASE. I would recommend your mother see her primary doctor to have this evaluated. Lyme's disease is a common disease, especially in the Northeastern United States -- but this would be a exceedingly rare symptom. Lyme's disease is a condition caused by a bacterial infection. The bacteria (known as Borellia) is transmitted by a tick bite (by the Ixodes tick). When the tick injects the bacteria into the body -- this can (but not always) cause Lyme's disease. There are some common symptoms of Lyme's disease. A rash (that looks like a spreading circle with a central white clearing area) is common at the site of the infection. Occasionally people have a facial droop known as Bell's Palsy. Joint pain is also fairly common. There are some people who develop Lyme's carditis -- often a slow heart beat. In general, fatigue and "feeling ill" are also commonly seen. Mood swings without any other symptoms (like those mentioned above) are not consistent with Lyme's disease. There are some blood tests (while not perfect) that could help diagnose this. Talk to your doctor for more information. Good luck!