To examine the influence of mode of illness onset on psychiatric
status and neuropsychological performance, 36 patients with
CFS were divided into two groups: sudden vs gradual onset of
symptoms. These two CFS subgroups were compared to each other
and to sedentary healthy controls on standardized
neuropsychological tests of attention/concentration,
information processing efficiency, memory, and higher cortical
functions. In addition, the distribution of comorbid Axis I
psychiatric disease between the two CFS groups was examined.
The rate of concurrent psychiatric disease was significantly
greater in the CFS-gradual group relative to the CFS-sudden
group. While both CFS groups showed a significant reduction in
information processing ability relative to controls,
impairment in memory was more severe in the CFS-sudden group.
Because of the significant heterogeneity of the CFS
population, the need for subgroup analysis is discussed.