Idiopathic systemic capillary leak syndrome and related shock in PICU: an underdiagnosed disease?

Background: Idiopathic systemic capillary leak syndrome (SCLS), or Clarkson syndrome, is a rare disorder characterized by increased capillary permeability causing fluid leakage into interstitial spaces. SCLS remains underdiagnosed in both adults and children due to its resemblance to septic shock, with particularly limited pediatric data available. Methods: We conducted a retrospective analysis of six pediatric patients with seven SCLS episodes diagnosed in two Italian PICUs over a ten-year period. Results: Patients aged 4-10 years presented with hypovolemic shock and the characteristic triad of hypovolemia, hemoconcentration, and hypoalbuminemia without albuminuria. No monoclonal gammopathy was observed. Viral infections (75%, predominantly influenza) were identified as triggers. Common complications included rhabdomyolysis (100%), compartment syndrome (100%), acute kidney injury (71.4%), and cardiac involvement (71.4%). Cardiothoracic index measurements showed significant elevation during acute phases (mean 58% ± 1%) with reduction after treatment (mean 51% ± 1%). Mean hospitalization was 20 days (12 in PICU). One patient died from refractory ventricular fibrillation, another experienced recurrence. Conclusions: Pediatric SCLS represents a severe condition with distinctive characteristics compared to adult cases, including absence of monoclonal gammopathy, frequent viral triggers, and universal complications of rhabdomyolysis and compartment syndrome. Early recognition using our proposed diagnostic red flags can facilitate prompt intervention and improve outcomes.