A young adult with post-traumatic breathlessness, unconsciousness and rash

Discussion

Fat embolism to the pulmonary circulation invariably occurs with major trauma, including elective surgical procedures such as intramedullary nailing of long bones; however, these are usually asymptomatic and resolve on their own. However, it may (0.5–11% of cases) [1, 2] progress to a systemic inflammatory cascade affecting multiple organ systems, where morbidity and mortality is high, known as FES.

Diagnosis of FES is, by and large, clinical and is characterised by the triad of hypoxaemia (95%), neurological dysfunction (60%) and petechial rash (33%) [3]. In our case, the initial presentation of post-traumatic dyspnoea and hypoxia along with imaging were indicative of pulmonary contusion with pneumothorax leading to ARDS. However, the development of altered mental status without obvious head injury and subsequent appearance of rash rightly pointed our diagnosis to FES. The classic triad is usually not present in all patient, requiring the presence of at least one major and any four of the minor criteria for diagnosis, as was proposed by Gurd (table 1) [3–6]. The presence of all the features of the classical triad makes our case an interesting one.

Features of FES develop in a subacute manner, usually 12 h after the initial insult, peaking at 48–72 h [7], which was observed in our case. Pulmonary manifestations are the most common initial signs, such as breathlessness, tachypnoea, hypoxaemia and respiratory failure, which were observed in our case. The radiological findings, such as the patchy ground-glass opacities associated with interlobular septal thickening on chest HRCT, were also supportive.

Neurological abnormalities vary greatly, ranging from headache, irritability, confusion to coma, and rarely include seizures and focal findings [8]. They may occur as a consequence of hypoxaemia or cerebral embolism. Generalised seizure in our case is an intriguing observation because this is very rare occurrence in FES [9]. Specific findings on neuroimaging are strongly supportive. CT scans are frequently normal in these patients. However, the characteristic MRI finding is the star field pattern, demonstrating scattered foci of high-intensity restricted diffusion on DWI [6, 8, 10] reflecting acute ischaemia and cytotoxic oedema, as in our case. This is most apparent in the acute phase, from 4 h to the first few days from the time of injury [9].

Skin changes revealed petechial rash, typically over the upper trunk, axillary regions and conjunctiva [4, 6], which was evident in our case.

Although the pathophysiology of FES remains poorly understood, two main theories were proposed. Firstly, increased intramedullary pressure after an injury causes fat droplets to be released into the venous system, which then travel through a shunt such as patent foramen ovale (PFO) or may directly filter through pulmonary capillary bed into the ­arterial circulation (mechanical theory). Therefore, PFO should be considered an additional risk factor for cerebral fat embolism but is not necessary for the syndrome [8]. In our case, PFO was excluded by transthoracic colour Doppler echocardiography. Another theory (biochemical) is that bone marrow fat metabolised by tissue lipase produces pro-inflammatory free fatty acids, leading to end-organ dysfunction [6]. FES may happen in nontrauma situations like acute pancreatitis, sickle cell disease and lipid infusion [6, 8].

Currently, there is no disease-specific treatment for FES; supportive intensive care is the mainstay of therapy. Heparin and corticosteroids have been proposed as treatments but have not reliably demonstrated improved morbidity or mortality. Early surgical fixation (within 24 h of trauma) carries a lower risk of FES than delayed fixation.