Case Presentation: A 36-year-old woman with past medical history of depression and sickle cell trait presented to the hospital with two days of fevers and chills. She was treated for streptococcus A pharyngitis with clindamycin one month prior to presentation, but at this time had no other symptoms. On presentation, her exam was notable for fever, tachycardia, tenderness of the left anterior neck, and aphthous oral ulcers. Laboratory results were significant for an absolute neutrophil count (ANC) of 0. Upon further review of the medical record, the patient had intermittent neutropenia for the prior four years with ANC ranging from 0.5 to 7.7, but never as low as 0. A basic infectious and metabolic workup was previously done and yielded no identifiable etiology. This admission, an extensive work-up was conducted beyond common causes including a comprehensive evaluation of infectious causes, autoimmune markers, bone marrow biopsy, genetic chromosomal analysis and next generation sequencing myeloid panel, which were all negative. Given the severity of her neutropenia and lack of other findings, an anti-neutrophil antibody test was sent out, which later confirmed a diagnosis of autoimmune neutropenia. She was treated with 60mg of oral prednisone followed by a steroid taper for a total of four weeks with normalization of her ANC.
Discussion: Neutropenia is defined as an ANC less then 1,500 cells per microliter and is a common problem for the hospitalist. Neutropenia is typically related to an obvious cause, such as malignancy, chemotherapy, or a preceding infection. However, patients with repeated or prolonged neutropenia without a clear cause should prompt additional evaluation. In comparison to the pediatric population where neutropenia is a common and often benign self-limiting condition, in adults it can be much more severe and usually associated with other auto-immune conditions. Primary autoimmune neutropenia in adults is rare, it most commonly affects females and is due to anti-neutrophil antibodies. Despite the difference in etiology, the presentation is identical to other causes, hence the difficulty in evaluation. One confounding factor for this patient was recent treatment with clindamycin, one of many drugs associated with neutropenia. However, the severity and chronicity of neutropenia was out of proportion to the antibiotic exposure, leading to further investigation. The management of autoimmune neutropenia is also similar despite etiology. Antibiotic administration according to hospital guidelines is a mainstay prior to diagnosis, and investigation for more common causes is appropriate prior to further testing. Given the rarity of the condition and dearth of clinical data no standard of care currently exists. Granulocyte colony-stimulating factor is commonly used for treatment but was not utilized in this case as the patient’s bone marrow biopsy showed adequate reserve and it was therefore not expected to be effective. This patient responded to prednisone, with resolution to a normal ANC.
Conclusions: Primary autoimmune neutropenia is a rare etiology of neutropenia in adult patients. Suspicion for this diagnosis should rise once common etiologies are excluded, particularly in repeated cases without an identified etiology. Although no standard guidelines currently exist for management, a course of high-dose prednisone was effective for this patient and should be considered for others going forward.