JMIR Publications

ABSTRACT

Background:

A common definition of "subthreshold" is that the diagnostic threshold is not met; however, individuals are not asymptomatic. Some symptoms are present, causing significant difficulty in functioning and negatively impacting quality of life. Despite the attention given to subthreshold symptoms and the interventions for subthreshold symptoms being efficient in preventing the transition to psychiatric disease in primary care, reports on specific interventions are insufficient.

Objective:

This study aimed to verify the feasibility and effectiveness of internet-delivered cognitive behavioral therapy (ICBT) for subthreshold depression (SD), subthreshold insomnia (SI), and subthreshold panic (SP).

Methods:

Participants, aged 18–70 years, acting as internet research monitors were categorized into SD, SI, and SP groups based on screening assessments on the Center for Epidemiological Studies Depression Scale (CESD), Pittsburgh Sleep Quality Index (PSQI), and Panic and Agoraphobia Scale (PAS). They were randomly assigned to intervention or control groups within each category. The intervention included 4 weeks of non-guided ICBT (Mentre). Primary outcomes were the difference in mean change scores between screening and 4-week follow-up on the CESD in the SD group, PSQI in the SI group, and PAS in the SP group. Secondary outcomes were the amount of change from screening to post-evaluation and 4-week follow-up in all groups regarding the CESD, PSQI, PAS, and, Generalized Anxiety Disorder-7, Patient Health Questionnaire 9. They were analyzed using complete-cases analysis and repeated-measures analysis of variance. Additionally, the minimally important change in the primary endpoint for each group was also calculated as exploratory outcomes.

Results:

The SD, SP, and SI groups contained 846, 597, and 1,106 participants, respectively. In the SD group, the difference in change score of CESD from baseline to follow up between the intervention and control groups were significant (difference, 0.52; 95% CI, 1.29–4.66; P<.001). In the subthreshold insomnia group, differences in change score of PSQI were also significant (difference, 0.53; 95% CI, 0.11–0.94; P=.01). Regardless of that in the subthreshold panic group, differences in change score of PAS were not significant (difference, 0.07; 95% CI, -2.00–2.15; P=.94).

Conclusions:

The SD, SP, and SI groups contained 846, 597, and 1,106 participants, respectively. In the SD group, the difference in change score of CESD from baseline to follow up between the intervention and control groups were significant (difference, 0.52; 95% CI, 1.29–4.66; P<.001). In the subthreshold insomnia group, differences in change score of PSQI were also significant (difference, 0.53; 95% CI, 0.11–0.94; P=.01). Regardless of that in the subthreshold panic group, differences in change score of PAS were not significant (difference, 0.07; 95% CI, -2.00–2.15; P=.94). Clinical Trial: University Hospital Medical Information Network (UMIN) registration number (UMIN000051280).