Anaphylaxis followed by unilateral lung opacity and hypocomplementemia in a young female

A 36-year-old woman was stung in the right wrist by a bee, suffered typical anaphylaxis, and was transferred to a local hospital. After a few hours, which corresponded to late-onset reaction, she developed shortness of breath and weakness and was transferred to the emergency department, where the diagnosis of anaphylaxis was confirmed. Serum complement levels, components C3 and C4, were undetectable. Flexible bronchoscopy excluded lung hemorrhage. She was on the ventilator for 4 days and was fully awake during that time. After the treatment, her improvement was rapid, and she fully recovered. Three weeks after she had been stung by a bee, skin prick tests to bee, wasp, and yellow jacket venom were done, and all tests came back negative as well as IgE and IgG4 antibodies to the same venoms. Coagulation factors and the complement, including C1q inhibitor, were normal. Occurrence of complement activation and consumption could point to the immune complexes as basis of pathophysiological mechanism. It remains unclear why such a reaction would involve only the right lung and why no detectable immune complexes were discovered. The clinical picture in the presented case resembled acute respiratory distress syndrome, but the exact nature of lung consolidation remains puzzling. The most likely explanation is a very rare case of airway obstruction. To our knowledge, this is the only reported case of anaphylaxis associated with undetectable serum complement levels. The potential role and diagnostic significance of hypocomplementemia in cases of anaphylaxis should be further investigated.