The Fever Files: Hot to Clot
The Case
The countdown to the end of shift is on when the tones go off and your relief is nowhere in sight. You drag yourself to your ambulance and, resigned to finishing your shift late (again), radio that you are en route.
The dispatcher sounds guilty to have sent you out at the end of the day, exuding regret in his voice as he gives you details: 37-year-old woman with a leg infection 15 minutes away (in, of course, the opposite direction of the closest hospital).
Your patient meets you at the door. She seems winded, but otherwise well. She starts to volunteer a history:
“My leg has been hot and red and swollen for the last few days. It’s getting worse, and I can barely walk. It hurts, and I can only take a few steps before I have to sit down.”
She complains of fever and cough, no sputum production, and a sharp chest pain with coughing.
Your partner quickly slaps on the monitor and collects a set of vitals:
- HR 116 sinus
- RR 18
- O2 sat 95% room air
- BP 132/82
- Temp 101.1 F (38.4 C)
Her cardiorespiratory exam is otherwise unremarkable, and her abdomen isn’t tender. Her left leg is swollen, and her calf is tender on exam. Her skin is discolored but doesn’t look indurated, and there are no open wounds.
She has a history of anxiety and depression, for which she is on bupropion. She doesn’t take any other medications, including birth control. She doesn’t smoke and she drinks alcohol socially, about 1-2 glasses weekly. You ask questions about cardiac ischemia, but she says no to them all; same when you explore a history of asthma. Her ECG is sinus tach but does not show signs of pericarditis.
You’re curious, but you’re also at the end of the day; you decide to load up and head to the hospital and make the differential diagnosis someone else’s problem.
En route to hospital, she becomes more tachycardic and her oxygen saturation falls to 92%. You reach for nasal prongs while you second guess your passive approach to this call. Is this just cellulitis, or is something more sinister occurring?
Thrombosis as a Cause of Fever
We can all fall prey to a bias called “early diagnostic closure.” Prematurely jumping to (and holding on to) a presumptive diagnosis can lead us all astray, even when evidence mounts that we are on the wrong track.
Fever = infection is one of those diagnostic traps. So is a seemingly isolated extremity physical finding. This is a case of a deep vein thrombosis of the leg migrating to the pulmonary artery causing pulmonary embolism. Thrombus can cause fever through triggering an inflammatory response or through pulmonary infarction. Up to a third of PE present with low grade fever.
While the patient’s symptoms started in her leg, they didn’t stay there; yet the medic in this case had his guard down, was tired, was rushing, and fixated on a hot, swollen leg.
In order to avoid this cognitive bias, it’s important to have a preconstructed differential diagnosis and line of inquiry (questions, physical exam, diagnostic tests) to increase assessment “data points.” When a data point seems to be an outlier, clinicians should double down on curiosity rather than throw the data point away. In our case, the winded breathing was not consistent with cellulitis, nor was the chest pain, which may have been discounted as anxiety.
Here's a short, high-yield list of noninfectious causes of fever to program into your differential diagnosis:
- Thrombosis
- Intracranial hemorrhage
- Hyperthyroidism
- Pancreatitis
- Drug reactions
- Alcohol withdrawal
- Hematologic cancers
- Autoimmune disease
Back to the Case
The triage nurse is fresh—she’s just started her night shift. When you start with the leg pain and redness, she stops you abruptly when she sees the nasal prongs and asks for a set of vitals. Despite being on 3L/minute, you’re ashamed to have not noticed that her O2 sat dropped lower, to 91%, and her heartrate climbed to 136.
“How does your chest feel” asks the triage nurse.
“It hurts … when I breathe” the patient says, appearing more labored than on scene. The triage nurse directs you to an acute bed while you crank up the tank to 5L.
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