Table 3

Summary of items included in the JDM optimal dataset, form A (completed at first/baseline visit only)

Section heading	Items		Additional items conditional on previous response (summary)
Personal factors/demographics	1	Date of birth (year and month of birth±day of birth)
Personal factors/demographics	2	Sex of patient
Diagnostic factors	3	Date (year and month) of first symptom of myositis
	4	Date (year and month) of diagnosis of JDM
	5	At the time of diagnosis did the patient have proximal muscle weakness?
	6	At the time of diagnosis did the patient have typical skin features of JDM (Gottron’s/heliotrope)?
	7	Was an MRI scan done at diagnosis?	Choice of options for MRI result (four options)
	8	Was a muscle biopsy done at diagnosis?	Choice of options for biopsy result (four options plus total biopsy score if available)
	9	Were myositis-specific antibodies tested at diagnosis?	If positive, asked to select all that apply (eight options)
	10	Were myositis-associated antibodies tested at diagnosis?	If positive, asked to select all that apply (nine options)
Treatments received prior to diagnosis of JDM	11	Did this patient receive systemic glucocorticoid prior to diagnosis of JDM?	If yes, asked to select all that apply (three options)
Treatments received prior to diagnosis of JDM	12	Did this patient receive any synthetic or biologic disease modifying anti-rheumatic drug prior to the diagnosis of JDM?	If yes, asked to select all that apply (13 options)