How does juvenile onset Idiopathic Inflammatory Myopathies differ from adult onset one?
- • JDM (95% of juvenile IIM): 65% have an MSA. No increase in malignancy risk. There is increase in calcinosis, gastrointestinal infarcts.
- Anti-NXP2 (MJ) (18%–25%): more calcinosis, weakness, cramps, atrophy, and contractures. No cancer association. Poor prognosis
- Anti-TIF1γ (p155/140) (23%–35%): no cancer association. More severe skin disease, photosensitivity, and lipodystrophy.
- Anti-MDA5 (CADM-140) (7%–36%): severe ILD (Asians), skin disease with ulcers, mild muscle disease.
- Anti-Mi2 (5%–10%): significant skin and muscle disease but good response to therapy.
- • Other myositis: rule out other causes of muscle disease like muscular dystrophies. Rarely children can have ASA syndrome (usually adolescents with anti-Jo-1) or IMNM with anti-SRP or anti-HMGCR (200/100 kDa).