This is a case report of an 8-year-old boy who developed an atypical, rare subphenotype of autoimmune inflammatory acute juvenile dermatomyositis (JDM), initially masquerading as viral polymyositis (PM)-like presentation, that was complicated by a hitherto unreported fulminant, life-threatening pediatric systemic capillary leak syndrome (SCLS). We highlight the close differential between viral PM and JDM, the baffling clinical syndromic constellation of hypotension with hemoconcentration - a "shock"-like syndrome, hypoalbuminemia without albuminuria, and generalized edema with the atypical JDM presentation, and stress crucial need to implement early aggressive, multipronged immunomodulatory treatment along with intensive fluid resuscitation which saved the life, this patient from a stormy, and turbulent 4-week clinical illness. This is the first published case description in the current literature of the association of an aggressive subphenotype of JDM and life-threatening pediatric SCLS. This report opens the Pandora's Box to explore the genetic and pathomechanisms of both disorders.