Pulmonary arterial hypertension in infancy: A case series.

Thiamine deficiency is a reversible cause of severe pulmonary arterial hypertension (PAH) in early infancy, particularly among exclusively breastfed infants of mothers consuming polished rice-based diets. This retrospective case series (July 2023-July 2025) included infants aged-12 months with echocardiographically confirmed severe PAH and no structural heart disease. Eight exclusively breastfed infants (median age 2.5 months) presented with respiratory distress. All mothers consumed polished rice-based diets. Echocardiography revealed severe PAH with right-sided cardiac dilation. Thiamine therapy resulted in rapid clinical improvement within 48 h and complete resolution within two weeks, with no deaths. Thiamine deficiency should be suspected in infants with acute severe PAH, as prompt treatment leads to excellent outcomes.