Table 1.

Demographic, clinical and serological features (n = 101)

Feature	Summary statistic
Gender, n (%) M:F	33 (32.7):68 (67.3)
Ethnicity, n (%)
White	72 (71.3)
Black	12 (11.9)
South Asian	8 (7.9)
Other	9 (8.9)
Clinical features, median [interquartile range]
Age at onset (years)	6.1 [3.9–9.3]
Time from disease onset to diagnosis, (months)	2.6 [1.5–7.5]
Time from diagnosis to biopsy, (months)	0.72 [0.39–0.92]
On steroids at biopsy, n (%)	12 (12.2)
CMAS at biopsy	29 [18.75–45]
Reported clinical diagnosis, n (%)
Definite or probable juvenile dermatomyositis	88 (88)
Juvenile dermatomyositis overlap with scleroderma	2 (2)
Juvenile dermatomyositis overlap with polyarthritis	6 (6)
Definite or probable Juvenile polymyositis	2 (2)
Focal myositis	1 (1)
Mixed connective tissue disease	1 (1)
Other idiopathic inflammatory myopathy	1 (1)
Antibody Status, n	90 of 101
Myositis‐specific autoantibodies, n (%)	53 of 90 (58.9)
Anti‐TIF1γ	18 (20.0)
Anti‐NXP‐2	15 (16.7)
Anti‐MDA5	11 (12.2)
Anti‐Mi2	5 (5.6)
Anti‐SRP	2 (2.2)
Anti‐PL7	1 (1.1)
Anti‐SAE	1 (1.1)
Myositis‐associated autoantibodies, n (%)	9 of 90 (10.0)
Anti‐PM‐Scl	6 (6.7)
Anti‐U1RNP	2 (2.2)
Anti‐Scl70	1 (1.1)
No identifiable autoantibodies, n (%)	28 of 90 (31.1)

Autoantibody status data were available in 90 cases. Percentages reflect the number of patients with a given antibody as a proportion of total tested patients.

CMAS, Childhood Myositis Assessment Scale.