Table 1 Demographic table of the sample study groups at the first study visit after June 1^st, 2018 (baseline). The age of onset, sex, EULAR/ACR diagnostic certainty criteria, baseline features, treatment medications), and myositis specific / associated autoantibodies (MSA/MAA) are included for both the whole group (prevalence) & separately for the sub-group of the incidence cohort. One subject had both antiRo52 and anti-Jo-1, all others had no, or only one autoantibody. Autoantibody testing was performed using an immunoblot assay

Age of Onset – years

Mean (SD)

8.2 (4.1)

9.5 (4.1)

Range

1–16

3–16

Sex (%)

Female

66.2%

66.7%

EULAR/ACR

Diagnostic Certainty

- no. of patients (%)

Definite – 75 (97%)

Probable – 2 (3%)

Definite – 24 (96%)

Probable – 1 (4%)

Diagnostic features of the “Probable Patients”

Skin rash, positive autoantibodies, Abnormal Gottron’s papules, chest pain, respiratory discomfort, fatigue, poor sleep, reduced strength & muscle atrophy

Baseline Features at the first visit after June 1^st 2018

(Mean ± SD) or (%)

Manual Muscle Testing of 8 groups

(MMT-8, possible range 0 – 80)

(N = 32)

72.1 ± 10.0

(N = 20)

69.4 ± 10.6

Childhood Myositis Assessment

Scale (CMAS, possible range 0 – 52)

(N = 72)

44.9 ± 10.7

(N = 24)

39.8 ± 13.2

Childhood Health Assessment Questionnaire (CHAQ, possible range 0 – 3)

(N = 26)

0.7 ± 0.8

(N = 17)

1.0 ± 0.8

Disease Severity at Onset

by means of the Physician’s skin VAS (possible range 0 – 10)

1.8 ± 2.1

3.6 ± 1.9

Skin Ulcers*

Normal / None – 67 (87%)

Abnormal – 9(12%)

Missing—1

Normal / None – 19 (76%)

Abnormal – 6(24%)

Gottron’s Papules*

Normal / None – 41 (53%)

Abnormal – 35(45%)

Normal / None – 3 (12%)

Abnormal – 22(88%)

Heliotrope Rash*

Normal / None – 44(57%)

Abnormal – 32 (42%)

Normal / None – 6 (20%)

Abnormal – 19 (80%)

Nailfold Capillary*

Normal / None – 30(39%)

Abnormal – 46 (60%)

Normal / None – 4 (16%)

Abnormal – 21 (84%)

Treatment Medications

- no. of patients (%) on Tx at first visit after June 1, 2018

Prednisone

23 (30%)

15 (60%)

Methotrexate

37 (48%)

14 (56%)

IVIG

11 (14%)

2 (8%)

Hydroxychloroquine

5 (6%)

1 (4%)

Cyclophosphamide

1 (1%)

1 (4%)

Cyclosporin

0 (0%)

0 (0%)

MMF

0 (0%)

0 (0%)

Myositis Specific / Associated Autoantibodies (MSA/MAA) – no. of patients at any time (%)

Number tested = 40

Number tested = 22

Extractable nuclear antigen

(Anti-Ro52/SSA)

6 (15%)

4 (18%)

Melanoma Differentiation-

Associated gene 5 (Anti-MDA-5)

2 (5%)

1 (5%)

Transcription Intermediary

Factor 1(Anti-TIF-1)

1 (3%)

1 (5%)

Anti-histidyl transfer RNA [t-RNA] synthetase (Anti-Jo-1)

1 (3%)

1 (5%)

Nucleosome Deacetylase Complex; helicase binding protein (Anti-Mi-2)

0 (0%)

0 (0%)

Nuclear matrix protein 2 (Anti-NXP2)

0 (0%)

0 (0%)

All negative

30 (75%)

15 (68%)