D1.29 - When Anaphylaxis Is Not Anaphylaxis: A Rare Differential Diagnosis in Perioperative Shock

Background

Perioperative anaphylaxis is a rare but potentially life-threatening condition caused by IgE- and non-IgE-mediated mast cell activation. Diagnosis relies on clinical features, laboratory biomarkers and a structured allergy work-up. However, perioperative shock with atypical presentation and poor response to adrenaline should prompt consideration of alternative diagnoses. We report a case referred for suspected perioperative anaphylaxis that ultimately revealed an underlying congenital myopathy, highlighting the importance of rare non-allergic conditions in the differential diagnosis.

Case report

A 48-year-old male with longstanding muscle stiffness, exercise-induced cramps and episodic weakness was referred following perioperative shock during induction of general anesthesia. Approximately 20 minutes after induction, he developed severe hypotension and tachycardia, refractory to fluids, ephedrine and phenylephrine. Intravenous adrenaline led to only transient and incomplete hemodynamic improvement, requiring repeated boluses. No cutaneous, respiratory or mucosal manifestations were documented.

Clinical data was retrospectively collected from medical records. Laboratory evaluation included complete blood count, total serum IgE and baseline serum tryptase. Allergy testing comprised skin prick tests (SPT) and intradermal tests (IDT) using recommended concentrations, according to ENDA/EAACI guidelines. Genetic testing was performed after identification of a pathogenic variant in a first-degree relative. Subsequently, neuromuscular assessment (electromyography and muscle biopsy) and cardiac evaluation (transthoracic echocardiography and 24-hour Holter monitoring) were conducted.

Laboratory evaluation revealed a normal complete blood count, total serum IgE of 25.40 kU/L and baseline serum tryptase of 5.7 µg/L. SPT and IDT with propofol, rocuronium, lidocaine, ropivacaine, cefazolin and fentanyl were negative, as were latex SPT.

Genetic testing identified the same heterozygous pathogenic CLCN1 variant previously detected in the patient’s daughter, confirming autosomal dominant congenital myotonia. Cardiac evaluation was unremarkable. Electromyography showed myopathic features, while muscle biopsy was non-diagnostic.

Conclusion

Perioperative shock is not synonymous with anaphylaxis. In the absence of multisystem allergic manifestations, normal biomarkers and negative allergy testing, poor response to adrenaline should raise suspicion for rare non-allergic conditions such as congenital myopathies, preventing misdiagnosis and inappropriate drug allergy labeling.