(covers information from several alternate timelines)
Irumodic Syndrome was a degenerative neurological disorder that caused deterioration of the synaptic pathways. The condition caused confusion, delusions, and eventually death. It could take several years to develop and several more before it proves deadly. The treatment of choice in 2370 was peridaxon, though this only relieved the symptoms. Genetic testing could determine if a person may develop Irumodic Syndrome in later life, but not all persons who test positive would develop the condition.
In the anti-time future, Jean-Luc Picard had contracted advanced Irumodic Syndrome. His condition caused many of his friends to doubt his claims that he has been shifting back and forth through time. In this time period, no cure was known to exist.
In the anti-time past, while seeking evidence that he could already have Irumodic Syndrome, Picard was informed by Doctor Beverly Crusher that while he did not have the disease itself, he did have a small structural defect in his parietal lobe that could lead to a number of neurological disorders, including Irumodic Syndrome. The defect was so small it required a level-4 neurographic scan to be located. (TNG: "All Good Things...")