App-Based Self-Management for Somatic Symptom Disorder and MUS: A Pilot Study

Somatic symptom-related cognitive, affective, and behavioral distress will be assessed using the Somatic Symptom Disorder B-Criteria Scale (SSD-12). The SSD-12 is a 12-item self-report measure that evaluates the psychological B-criteria of somatic symptom disorder, including excessive health-related thoughts, negative emotions, and maladaptive behaviors in response to somatic symptoms. Each item is rated on a 0-4 scale, with higher scores indicating greater somatic symptom-related psychological distress.

Depressive symptoms will be measured using the Patient Health Questionnaire-9 (PHQ-9). The PHQ-9 is a 9-item self-report scale that assesses the frequency of core depressive symptoms over the past week, with items rated from 0 ("not at all") to 3 ("nearly every day"). Total scores range from 0 to 27, with higher scores indicating more severe depressive symptoms.

Anxiety symptoms will be assessed using the Generalized Anxiety Disorder-7 (GAD-7). The GAD-7 is a 7-item self-report questionnaire that measures the severity of generalized anxiety symptoms over the past week, with each item rated from 0 ("not at all") to 3 ("nearly every day"). Total scores range from 0 to 21, with higher scores indicating greater anxiety severity.

Social anxiety symptoms will be measured using the self-rated version of the Liebowitz Social Anxiety Scale (LSAS-SR). The LSAS-SR consists of 20 items assessing fear and avoidance across a range of social and performance situations, with each item rated on 0-4 scales for fear and avoidance. Higher scores reflect more severe social anxiety and greater avoidance of social situations.

Trait mindfulness will be assessed using the Korean version of the Five Facet Mindfulness Questionnaire - Short Form (FFMQ-SF). The FFMQ-SF is a 15-item self-report scale that evaluates five facets of mindfulness: non-reactivity, observing, acting with awareness, describing, and nonjudging. Items are rated on a 1-7 scale, with higher scores indicating higher levels of dispositional mindfulness across these facets.

Psychological acceptance will be measured using the Korean version of the Acceptance and Action Questionnaire-II (AAQ-II). The AAQ-II is a self-report measure that assesses acceptance of internal experiences and willingness to act in line with values in the presence of difficult thoughts and feelings. Items are rated on a Likert-type scale, and in the Korean scoring used in this study, higher scores indicate a higher level of acceptance and openness toward internal experiences.

Cognitive emotion regulation strategies will be assessed using the Cognitive Emotion Regulation Questionnaire (CERQ). The CERQ is a 35-item self-report measure that evaluates nine cognitive strategies used in response to negative life events, including acceptance, putting into perspective, positive refocusing, refocus on planning, positive reappraisal, self-blame, catastrophizing, other-blame, and rumination. Items are rated on a 1-5 scale, with higher subscale scores indicating more frequent use of the corresponding cognitive emotion regulation strategy.

Intolerance of uncertainty will be measured using the 12-item Intolerance of Uncertainty Scale - Short Form (IUS-12). The IUS-12 assesses negative beliefs, distress, and difficulty functioning in situations involving ambiguity or uncertainty, with items rated on a 1-4 scale. Higher scores indicate greater intolerance of uncertain or ambiguous situations.

Self-criticism and self-reassurance will be assessed using the Korean version of the Forms of Self-Criticism/Attacking and Self-Reassuring Scale (FSCRS). The FSCRS is an 18-item self-report measure that assesses two main dimensions: self-critical attitudes and self-reassuring responses toward oneself when facing setbacks or failures. Items are rated on a 0-4 scale, with higher scores on self-criticism indicating more frequent self-attacking, and higher scores on self-reassurance indicating a greater ability to respond to oneself with kindness and support.

Health-related attitudes and concerns will be measured using the Illness Attitudes Scale (IAS). The IAS is a 27-item self-report scale that assesses hypochondriacal concerns, health anxiety, disease conviction, and related illness attitudes. Items are rated on a 0-4 scale, with higher scores reflecting more negative or maladaptive attitudes and fears related to illness.

Interoceptive awareness will be assessed using the Korean Multidimensional Assessment of Interoceptive Awareness (K-MAIA). The K-MAIA is a 32-item self-report scale that measures multiple dimensions of how individuals perceive and relate to internal bodily sensations, including noticing, attention regulation, emotional awareness, self-regulation, and body listening. Items are rated on a 0-5 scale, with higher scores indicating more adaptive and accurate interoceptive awareness.

Perceived control and desire for control will be measured using the Korean version of the Shapiro Control Inventory (K-SCI), focusing on the positive control, negative control, and desire for control subscales. These subscales together comprise 24 items rated on a 1-7 scale and assess individuals' beliefs about their ability to exert control, their experiences of lacking control, and their motivation to maintain or increase control. Higher scores on each subscale indicate stronger positive sense of control, greater negative control experiences, or greater desire for control, respectively.

Perceived usability and acceptability of the mobile application will be assessed using a 24-item self-report questionnaire adapted from prior work on smartphone-based interventions for serious mental illness. Items are rated on a three-point scale (disagree, neutral, agree) and evaluate ease of use, perceived usefulness, satisfaction, and willingness to continue using or recommend the app. Higher scores indicate greater perceived usability, acceptability, and perceived value of the digital intervention.