Development of a conceptual model of early systemic sclerosis (scleroderma)

Systemic sclerosis (SSc) is a rare connective tissue disorder with heterogeneous manifestations. Two predominant subtypes, limited cutaneous SSc (lcSSc) and diffuse cutaneous SSc (dcSSc), are distinguished based on skin involvement distribution. A comprehensive conceptual SSc model is needed to support measurement strategies for outcome studies. This qualitative study aimed to explore key SSc disease concepts and develop a conceptual disease model capturing the heterogeneous lived experiences of patients with SSc.

Patient- and clinician-reported concepts specific to dcSSc (more severe and faster-progressing than lcSSc) were identified via a targeted literature review and used to develop a preliminary dcSSc symptom model and a semi-structured qualitative interview guide. The guide was used in concept elicitation interviews with adults with lcSSc and dcSSc. A final conceptual SSc symptoms model was refined based on interview results.

Disease concepts were retrieved from 35 peer-reviewed articles and 17 clinical trials focusing on patients with dcSSc. The preliminary dcSSc symptom model included skin, hand, gastrointestinal, pain, joint, muscle, mouth, sexual, lung, cardiovascular, cognitive, ocular, and other symptoms. During concept elicitation interviews, participants (n = 44) reported 112 unique symptoms (within 13 domains). Twenty-six symptoms had not previously been identified in pertinent literature. Hand and skin symptoms were reported by all participants. Over 95% of participants reported at least one gastrointestinal and pain symptom, around 80% reported joint and mouth symptoms, 70% reported muscle symptoms, and over 50% reported ocular symptoms. Cognitive, lung, sexual, and cardiac symptoms were reported by fewer than half of participants. Participants with dcSSc reported a broader variety of symptoms than those with lcSSc. However, concepts relevant to patients with dcSSc and lcSSc strongly overlapped, suggesting that a single conceptual model is appropriate to map symptoms for both subtypes. The overlap was further reflected in the most bothersome symptoms, which included skin fibrosis and hand symptoms for both populations.

The final conceptual model captures the heterogeneous symptoms of SSc and reflects the lived experience of patients with SSc. It covers both clinical SSc subtypes and can support the choice and/or development of instruments to measure patient experiences in clinical trials.