Case Presentation: A 38-year-old woman with a history of discoid lupus presented with a week of progressive fever, chills, pustular rash, and polyarthritis. The pustular lesions started periorally but then spread to the palms, soles, and torso. Her joint pain was predominantly in her ankles, knees, wrists, and shoulders. Aside from minor scratches from pet dogs and cats, she reported no significant exposures.On admission, she was afebrile with stable vitals. Examination showed a diffuse pustular rash including the palms and soles and a punctate lesion on the right second finger, which the patient attributed to a recent construction project. Joint tenderness was noted in the bilateral MCPs, wrists, ankles, and knees without synovitis. Labs revealed leukocytosis (24.4×10^9/L) and an elevated CRP (170.4 mg/L). Blood cultures were drawn. Given concern for disseminated gonorrhea, infectious disease was consulted who recommended initiating ceftriaxone and doxycycline. Tests for enterovirus, gonorrhea/chlamydia, syphilis, tick-borne illnesses, and HIV were negative. Autoimmune tests only showed a mildly positive ANA and RF, consistent with her known discoid lupus and active inflammation.After improvement of her rash, she was discharged with a 7-day course of empiric doxycycline. The next day, she contacted the service, now recalling that she had sustained a rat bite to her right second digit a few days prior to symptom onset, leading to a new diagnosis of rat bite fever. Her doxycycline course was extended, and her symptoms resolved in the following weeks.
Discussion: Here, we present a patient with fever and rash whose diagnosis was elusive. The differential for fever and rash is broad, but narrows when the rash involves the palms and soles, as in our case. Pustular palmar and plantar rashes are often linked to infections with coxsackie virus, secondary syphilis, disseminated gonorrhea, and Rocky Mountain Spotted Fever. Autoimmune causes include reactive arthritis and palmoplantar pustulosis. Rat bite fever is a rare disease caused by exposure to a rat colonized with Streptobacillus moniliformis. It typically presents with fever, polyarthralgias, and a rash that can involve the palms and soles. Given difficulty of culturing S. moniliformis, a presumptive diagnosis is made when a patient presents with fevers and a history of rat exposure with or without a bite. Prompt recognition and empiric treatment is crucial as mortality rate can be as high as 13%. Standard treatment is with penicillin, but doxycycline can be used in cases of penicillin allergy (as was the case in our patient). This case underscores the importance of thorough history taking and re-evaluation in the hospital for patients with systemic symptoms and a negative initial workup. It also highlights the potential for uncommon infections to mimic more common inflammatory and infectious conditions, such as hand-foot-mouth disease or disseminated gonococcal infection.
Conclusions: While rare, rat bite fever should be promptly recognized and treated when exposure and clinical presentation point to the diagnosis. Hospitalists play a critical role in piecing together evolving histories, as seen in this patient who recalled a rat bite only after discharge. Revisiting initial diagnoses is a critical skill within hospital medicine as new insights can lead to improved patient outcomes.