Deceptive Dyspnea: A Dual Pathology of Myasthenia Gravis and Right-to-Left Shunt Masquerading As Status Asthmaticus

Respiratory failure in myasthenia gravis (MG) can mimic refractory status asthmaticus, leading to misdiagnosis and delayed treatment. We present the case of a 28-year-old female with a history of asthma and a known partial atrioventricular canal defect who was admitted with acute respiratory failure and severe hypoxemia, not responsive to maximum bronchodilator and corticosteroid therapy. Fatigable weakness on bedside examination led to a diagnosis of seropositive generalized MG. Although treated with pyridostigmine and intravenous immunoglobulin to improve her muscle strength, the persistence of severe hypoxemia suggested an underlying pathology. Bubble contrast echocardiography then confirmed a right-to-left shunt via her cardiac defect, along with mild pulmonary hypertension, and thus a double pathophysiology for her respiratory failure. It highlights that a failure of the patient to improve as anticipated should prompt diagnostic reassessment to prevent anchoring bias, and it underscores the crucial role of contrast echocardiography in identifying disproportionate hypoxemia in patients with an underlying cardiac shunt.