Systemic lupus erythematosus mimicking Japanese spotted fever due to Rickettsia japonica detection in an eschar: a case report

Neuropsychiatric systemic lupus erythematosus (NPSLE) is a subset of systemic lupus erythematosus (SLE) characterized by neurological and psychiatric manifestations. NPSLE diagnosis requires exclusion of alternative etiologies, including infection. Rickettsial diseases exhibit features similar to those of SLE, including fever, rash, and cytopenia. In several reported cases, patients initially suspected of having rickettsial diseases were ultimately diagnosed with SLE. Recently, rickettsial DNA detection in eschars and/or blood using polymerase chain reaction (PCR) has been performed to diagnose rickettsial diseases. Herein, we report a case of NPSLE complicated by a concurrent localized Rickettsia japonica infection. The patient was a 43-year-old man residing in a Japanese spotted fever (JSF)-endemic region. He was transferred to our hospital because of respiratory failure and consciousness disturbance. Fever, cytopenia, and elevated liver enzyme levels were observed. Physical examination revealed eschars on the right thigh. The differential diagnoses were JSF and SLE. Treatment with minocycline and glucocorticoids improved the patient’s clinical status. Subsequently, R. japonica DNA was detected in eschar samples; however, convalescent antibody titers against R. japonica remained negative. The patient’s symptoms recurred after discontinuation of glucocorticoid therapy, accompanied by elevated titers of SLE-associated antibodies. This case highlights a rare instance of localized rickettsial infection, which should be considered in the differential diagnosis of febrile diseases in rickettsia-endemic areas, particularly in the context of PCR-based diagnostic approaches for rickettsial diseases.