Rickettsia parkeri Rickettsiosis Resembling Sweet Syndrome: A Differential Diagnosis for Critical Discussion.

Introduction: Spotted fever group (SFG) rickettsioses are tick-transmitted infections caused by Gram-negative, obligately intracellular bacteria in the genus Rickettsia. They present as an acute undifferentiated febrile illness, and they are often accompanied by rash and/or eschar. Although the rash of SFG rickettsioses usually consists of macules and papules, some, like in Rickettsia parkeri rickettsiosis, can also manifest with papulovesicular or pustular lesions. Case: We herein present a case of SFG rickettsiosis, due to R. parkeri, that masqueraded as Sweet syndrome (the prototype neutrophilic dermatosis) after the initial results of a shave biopsy. Further investigation of the biopsy specimen by immunohistochemical and PCR analysis would eventually confirm SFG rickettsiosis, with R. parkeri being detected by real-time PCR. Discussion:Rickettsia parkeri is transmitted by the Gulf Coast tick (Amblyomma maculatum) and is an increasingly recognized cause of SFG rickettsiosis in the United States. Rickettsia parkeri should be considered in those with an acute undifferentiated febrile illness with lesions that are pustular or papulovesicular, as prompt recognition and empirical administration of doxycycline results in the rapid resolution of symptoms.