Cognitive disengagement syndrome, or CDS, shares some features with attention-deficit/hyperactivity disorder, but a large survey suggests the two symptom patterns are not identical.
CDS describes experiences including daydreaming, mental fog, slowed thinking or behavior, drowsiness and low engagement. It was previously known as sluggish cognitive tempo. CDS is currently a research construct rather than a diagnosis listed in the DSM-5-TR or ICD-11.
What the Iranian survey found
The survey included 8,075 participants in Iran between the ages of 15 and 55. A subset of 2,012 participants also completed an ADHD questionnaire. The questionnaires measured symptoms; they were not diagnostic tests.
Among those who completed both questionnaires, total CDS and ADHD scores were strongly correlated, with a correlation of r = .69. The relationship was stronger between CDS and ADHD inattention, at r = .70, than between CDS and hyperactivity or impulsivity, at r = .53.
The overlap was substantial at the highest symptom levels. Of the people in the sample’s top 10% for CDS symptoms, 49% were also in the top 10% for ADHD symptoms. Conversely, 48% of those in the top 10% for ADHD symptoms were also in the top 10% for CDS symptoms.
Different symptom emphasis
The researchers reported differences between people who scored high only on CDS and those who scored high only on ADHD. The CDS-only pattern was associated with greater mental slowness and mind-wandering, while the ADHD-only pattern was characterized more by attention problems.
Mind-wandering was related to ADHD inattention, but the association was more modest than the overall CDS–inattention relationship, at r = .35. These findings suggest overlap without establishing that CDS and ADHD are separate diagnoses or proving that one causes the other.
A discriminant-function model classified 95.3% of people correctly. Its accuracy was 93.9% when tested with leave-one-out cross-validation. However, the researchers defined the groups using the same questionnaires that supplied the sorting scores, which may have increased the apparent classification accuracy.
Why the percentages do not show prevalence
Using a sample-based top-5% cutoff, 5.8% of all participants scored high for CDS symptoms. The cutoff was a score of 34 or higher and included 466 people. The researchers also reported other sample-based thresholds: 8.3% at the sample average plus 1.5 standard deviations and 11.3% at the top-10% level.
These figures describe how participants scored against thresholds created from this particular sample. They do not estimate the prevalence of CDS in Iran, and the thresholds have not been clinically validated.
Scores above the top-5% cutoff were more common among participants aged 15 to 17 than among older participants: 9.1% compared with 1.2% to 1.6% among those aged 35 to 55. Females scored above the cutoff more often than males, 6.4% versus 4.3%.
In a model that included age and sex, females had 1.46 times the odds of scoring above the cutoff, while each additional year of age was associated with an odds ratio of 0.94. Age and sex together explained about 9% of the variation in high CDS scores.
Because the survey examined people at one point in time and the older age groups were small, these results cannot show that CDS symptoms decline with age. The age comparisons involved different people rather than tracking the same participants over time.
How this fits earlier research
The findings are consistent with earlier work summarized in a 2016 meta-analysis of 73 papers involving more than 19,000 people. That analysis found that 13 CDS symptoms consistently grouped separately from ADHD symptoms in factor-analysis studies. It also reported stronger CDS links with ADHD inattention than with hyperactivity or impulsivity in both adults and children.
A nationally representative U.S. study of 2,056 children reported that about 2.6% were high on CDS only, 4.5% on ADHD only and 2.4% on both. Children in the CDS-only group had more anxiety, depression, shyness and sleep problems than those in the ADHD-only group.
What the study can—and cannot—establish
The Iranian survey recruited participants through schools, universities, workplaces, public centers and online links shared by word of mouth. About 70% of forms were completed online, and 70.8% of participants were female. These convenience and snowball recruitment methods mean the results may not represent Iran as a whole or apply to other countries.
The study relied on self-reported questionnaires and did not include clinical interviews, reports from family members or teachers, or objective measures of attention and processing speed. People who reported a history of major psychiatric disorder were excluded, as were incomplete or careless responses. Self-reported psychiatric history may not identify every relevant condition, and unrecognized sleep, medical or psychiatric problems could have affected scores.
The results add evidence that CDS symptoms overlap with ADHD symptoms while emphasizing different features. They do not establish CDS as a diagnosis, provide a population prevalence estimate or show that symptoms change with age.
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