Case of the Month #1 - Trauma

Published 03/02/2022

What is the most likely diagnosis?

This is likely to be Fat Embolism Syndrome (FAS).  It comprises of a triad of respiratory changes, neurological features and the development of a petechial rash.  The signs and symptoms are thought to occur as a result of micro-vascular fat emboli causing obstruction in the micro-circulation at various sites.  The mechanism by which this occurs is not well understood; it is thought to either be due to the direct entry of fat globules released following adipose damage or significant bony injury following trauma (mechanical theory) or via production of toxic intermediaries of fat present in the plasma (biochemical), or both.

It is most commonly seen after major trauma, particularly with closed fractures of the long bones and pelvis, and typically presents between 24 and 72 hours after the initial injury.  It can also occur due to trauma involving the soft tissues such as liposuction and burns, and bone marrow disruption including harvest and transplant.  There are also a number of non-trauma related causes, which include pancreatitis and bone tumour lysis.  Non-trauma related causes are less common however.  Overall mortality for FAS is between 5-15%.1

The diagnosis is made using major and minor diagnostic criteria as described by Gurd (figure 1).  At least one major and 4 minor criterion must be present to make the diagnosis.

Major Criteria Minor Criteria
Axillary or subconjunctival petechiae Tachycardia . 110bpm
Hypoxaemia Pa02 < 60mmHg, Fi02 = 0.4 Pyrexia > 38.5°C
CNS depression disproportionate to hypoxaemia Emboli present in the retina on fundoscopy
Pulmonary oedema Fat present in urine
  A sudden drop in haematocrit or platelet values
  Increasing ESR
  Fat globules in the sputum

Figure 1

Additional criteria have been developed including Lindeque’s and Schonfeld’s criteria to improve reliability.

Investigation findings that may aid diagnosis further include unexplained anaemia and thrombocytopenia, raised serum lipase and the presence of fat globules in cytological examination of the urine, blood and sputum.  Radiological findings are non-specific and include diffuse alveolar airspace shadowing on CXR and focal areas of ground glass shadowing on chest CT.

Treatment is entirely supportive.  Early immobilisation of fractures and operative fixation rather than conservative management reduces the incidence of FES. Respiratory involvement is almost universal and often requires invasive support to maintain oxygenation.  Haemodynamic support and replacement of blood and clotting products may also be required.  Corticosteroids, heparin and aspirin have all been investigated as potential treatment options for FES, but have not reliably demonstrated efficacy.

Despite a quoted mortality of between 5-15%, the prognosis of survivors is favourable with the respiratory and neurological symptoms resolving in most cases.