A 26-year-old man with a history of seizure disorder and medication nonadherence is hospitalized after a generalized tonic-clonic seizure. A witness reports that the patient lost consciousness and fell off a 15-foot ladder onto his right side; the seizure lasted about 2 minutes. Evaluation in the emergency department reveals a low serum level of his prescribed antiepileptic drug, levetiracetam, and a displaced right femur fracture. No other injuries or laboratory abnormalities are present. Levetiracetam is restarted and he undergoes intramedullary nailing of the fracture with no intraoperative complications. The next day the patient is noted to be confused. Temperature is 37.2 C (99 F), blood pressure is 142/86 mm Hg, pulse is 102/min, and respirations are 28/min. Oxygen saturation is 90% on room air. On physical examination, he is disoriented but has no focal weakness or sensory loss. There is no rash or hematoma at the surgical site. The remainder of the examination shows no abnormalities. Laboratory results are as follows:
| Complete blood count | |
| Hemoglobin | 12.4 g/dL |
| Platelets | 103,000/mm3 |
| Leukocytes | 9,000/mm3 |
| Serum chemistry | |
| Sodium | 136 mEq/L |
| Bicarbonate | 24 mEq/L |
| Creatinine | 0.8 mg/dL |
| Glucose | 118 mg/dL |
| Arterial blood gases | |
| pH | 7.47 |
| PaO2 | 58 mm Hg |
| PaCO2 | 34 mm Hg |
CT pulmonary angiography shows bilateral scattered ground-glass opacities but no filling defects within the pulmonary vasculature. Which of the following is the most likely cause of this patient's current condition?
Fat embolism syndrome | |
Etiology |
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Clinical presentation |
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Diagnosis |
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Prevention & treatment |
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This patient most likely has fat embolism syndrome (FES). The condition can occur 24-72 hours following fracture or surgical manipulation of bones that contain abundant marrow (eg, femur, pelvis). The marrow, consisting of fat and hematopoietic cells, embolizes into the venous circulation and can cause physical obstruction in the pulmonary capillaries. Some of the emboli may pass through the pulmonary circulation to cause microvascular occlusion in the systemic circulation (eg, brain, dermal capillaries). The circulating fat globules likely also induce a systemic inflammatory response that further contributes to microvascular dysfunction.
Patients with FES classically have the triad of respiratory distress (eg, tachypnea, hypoxemia), neurologic dysfunction (eg, confusion), and a petechial rash; however, the rash is present in less than half of cases. Thrombocytopenia may occur due to platelet adherence and aggregation to circulating fat globules. Patients typically develop pulmonary edema (mimicking acute respiratory distress syndrome [ARDS]) after 24-48 hours, seen in this patient by bilateral ground-glass opacities on chest CT scan. No pulmonary arterial filling defects are seen because the emboli obstruct the pulmonary capillaries and are too small to be detected on CT scan.
(Choice A) Aspiration pneumonitis is a chemical irritation of the lung parenchyma that can lead to ARDS and respiratory failure. It can occur in patients with periods of impaired consciousness (eg, seizure), but it is less likely in the absence of fever and leukocytosis. Thrombocytopenia would be unusual as well.
(Choice B) Cardiogenic pulmonary edema would explain this patient's respiratory distress; however, it would not explain the confusion unless cardiogenic shock is present. This patient's lack of hypotension rules out shock.
(Choice C) Drug-induced hypersensitivity in the form of drug reaction with eosinophilia and systemic symptoms (DRESS) is most commonly seen with certain antiepileptic medications (eg, lamotrigine, carbamazepine); however, levetiracetam is not a common culprit. Patients may have respiratory distress and confusion due to systemic organ involvement, but a macular rash is also expected because it is the most common manifestation of DRESS.
(Choice E) Pulmonary contusion results from chest trauma and involves localized pulmonary edema at the site of injury. The edema can take approximately 24 hours from the time of injury to develop; however, it is not expected to occur in a diffuse, scattered pattern, as in this patient.
Educational objective:
Fat embolism syndrome can occur following fracture of large, marrow-containing bones (eg, femur, pelvis). Patients classically have the triad of respiratory distress, neurologic dysfunction, and a petechial rash; however, the rash is present in less than half of cases.