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The Case

Chief complaint: fever and rash. I stare at the triage notes of the eight-year-old female I had just picked up. Overwhelmed by the vast differential that comes to mind, I decide to approach the case by first ruling out the most life-threatening diagnoses, such as meningococcemia and Stevens-Johnson syndrome, even though they are highly unlikely in my patient.

As an EM intern, I’m still developing a sense for distinguishing “sick” versus “not sick,” but upon entering my patient’s room, I know immediately this girl is “sick.” A thin, pale child lies before me, splayed out on the stretcher and holding her right arm across her chest. She doesn’t even look up when I introduce myself. A morbilliform rash peeks through her gown, and I notice the rash on her face, extremities, palms, and soles (see Figure 1). “Palms and soles…” I recall the more-focused differential for a palms/soles rash: meningococcemia; Rocky Mountain spotted fever; hand, foot, and mouth disease; secondary syphilis…

The parents describe their child as becoming progressively more “lethargic” and febrile over the past week (Tmax 104°F). They had already visited the pediatrician three times but decided it was time to come to the ED when the patient woke up refusing to walk due to pain in her knees and ankles. Delving into my bank of fever questions, I ask about headache, neck stiffness, skipped vaccinations, sick contacts, recent travel, or any new medications. However, all of these questions return negative. Fever, rash, joint pain—what else could I ask? At a loss, I decide to ask about any known tick bites, though this is unlikely because we are at the peak of winter in New England. Still negative. Any new pets? Well, now that I mention it, they admit to buying a new pet rat a few weeks ago.

(click for larger image) Figure 1. Morbilliform rash

On exam, the patient appears very fatigued. Her vital signs are significant for a fever of 38°C and heart rate of 126 bpm. Her respiratory rate, blood pressure, and SpO2 are within normal limits. The most striking exam findings are the patient’s pallor contrasted against a blanching morbilliform rash over her face, extremities, palms, and soles but sparing her torso. I also notice a petechial rash developing on the patient’s legs that I hadn’t seen previously. Despite mild postauricular lymphadenopathy, the rest of her head, eyes, ears, nose, and throat exam is normal. Her heart, lung, and abdomen exams are also normal. However, when I attempt to move the patient’s right shoulder and ankles, she moans in pain.

Rat-Bite Fever

As I return to my desk, the history of a new pet rat continues to resonate in my mind. I search the Internet for rat-borne diseases, and a recent news article appears as one of the top search results.¹ The article describes the case of a young boy misdiagnosed with a viral illness, but worsening of his symptoms resulted in his death a few days later. On autopsy, the boy was found to be infected with the bacterium causing rat-bite fever (RBF), Streptobacillus moniliformis.