What are the clinical features of fat embolism in adults with severe trauma or a history of orthopedic surgery?

Clinical Features of Fat Embolism Syndrome

Fat embolism syndrome presents with a classic triad of respiratory distress, neurological dysfunction, and petechial rash appearing 12-36 hours after long bone fractures or orthopedic surgery, though the condition can progress rapidly to life-threatening organ failure within hours. 1, 2

Timing of Presentation

• Most cases manifest within 24-72 hours post-trauma, with the classic triad appearing 12-36 hours after the initial injury 1, 2, 3
• Neurological manifestations typically occur 12-72 hours after the initial insult 4
• Fulminant presentations can cause devastating clinical deterioration within hours, progressing rapidly to cardiovascular collapse 1, 5
• Femoral shaft fractures operated within 10 hours show lower risk of fat embolism compared to delayed surgery 1

Major Clinical Features (Diagnostic Criteria)

The diagnosis requires at least one major criterion plus four minor criteria plus fat macroglobulinemia 2:

Respiratory System

• Hypoxemia and respiratory insufficiency are the dominant features, with progression to ARDS in severe cases 1, 2, 5
• Pulmonary involvement results from both vascular obstruction and inflammatory cascade activation 1
• Respiratory failure is predominantly a consequence of hemodynamic disturbances, with low cardiac output causing desaturation of mixed venous blood and ventilation/perfusion mismatch 1
• Pulmonary edema develops as part of the syndrome 5

Neurological System

• Altered mental status and central nervous system depression are hallmark features 1, 2, 5
• Cerebral involvement can present initially as isolated neurological manifestations before respiratory symptoms dominate 1, 2
• Acute confusional state is common 4
• Severe manifestations include cerebral infarction, spinal cord ischemia, hemorrhagic stroke, seizures, and coma 4
• Autonomic dysfunction and retinal ischemia may occur 4
• In Duchenne muscular dystrophy patients, CNS symptoms may be subtle or misinterpreted as agitation or panic 1

Dermatological System

• Petechial rash appears in the classic triad, typically in axillary or subconjunctival distribution 2, 5
• The rash is a major diagnostic criterion but may be absent in some presentations 4

Minor Clinical Features and Laboratory Findings

• Fat macroglobulinemia is a key diagnostic criterion, with fat globules found in blood, urine, sputum, bronchoalveolar lavage, or cerebrospinal fluid 1, 2
• Right ventricular failure is a critical determinant of clinical severity and outcome, with fulminant cases progressing to cardiovascular collapse 1
• Hemodynamic instability and circulatory shock can develop 1

Atypical Presentations and Diagnostic Pitfalls

• Cerebral fat embolism may occur without any respiratory or dermatological signs, making diagnosis challenging 4
• Fat embolism syndrome can present with isolated neurological manifestations initially 1, 2
• Many mild cases may recover unnoticed, as fat emboli develop in nearly all (>90%) patients with bone fractures but only 3-4% develop symptomatic FES 3, 5
• Diagnosis is often missed due to subclinical presentation or confounding injuries, requiring a high index of suspicion 2
• In Duchenne muscular dystrophy, FES should be considered after even minor trauma despite absence of radiological fracture evidence 1
• Even young, previously healthy individuals with initially stable presentations can experience rapid and fatal progression 6

Imaging Findings

• MRI of the brain shows characteristic findings and is of paramount importance in establishing diagnosis 3, 4
• CT scanning can show characteristic findings in some cases 7
• Contrast-enhanced CT may be needed to exclude massive pulmonary thromboembolism as a differential diagnosis 8

Clinical Course and Prognosis

• Most cases are self-limiting with appropriate supportive care, but the condition remains potentially fatal, especially with fulminant presentation 1
• The incidence of symptomatic FES is reported up to 30% in patients with long bone fractures, though many mild cases recover unnoticed 3
• Clinical deterioration can occur within hours, requiring aggressive early intervention 1
• Multiple organ system dysfunction develops due to either mechanical obstruction of capillaries by fat emboli or hydrolysis of fat to fatty acids 3