Irumodic Syndrome is a medical condition, a disease that affects the brain, making the patient suffer erratic behavior, delusions, loss of memory and other similar symptoms.
In Q's anti-time future, Jean-Luc Picard developed the disorder. In the anti-time 'present', Doctor Beverly Crusher informed Picard that he had a small defect in his parietal lobe that might one day lead to a number of different conditions, including Irumodic Syndrome. (TNG episode & novelization: All Good Things...)
In an alternate timeline, Picard also developed Irumodic Syndrome, although he continued to work on Project Phoenix. (DS9 - Millennium novel: The War of the Prophets)