American Board of Internal Medicine (ABIM) Certification Practice Exam

In lumbar puncture results for Rocky Mountain spotted fever, what finding is typically observed?

1. Neutrophilic predominance

2. Eosinophilic pleocytosis

3. Lymphocyte-predominant pleocytosis

4. Normocytic pleocytosis

The correct answer is: Lymphocyte-predominant pleocytosis

In the context of Rocky Mountain spotted fever (RMSF), the cerebrospinal fluid (CSF) analysis during a lumbar puncture typically reveals lymphocyte-predominant pleocytosis. This finding reflects a viral or rickettsial infection, where the immune response primarily involves T-lymphocytes. In RMSF, which is caused by the bacterium Rickettsia rickettsii, patients may present with a clinical picture that includes fever, rash, and neurological symptoms. The resultant inflammation in the CNS often leads to an increase in lymphocytes, which are a type of white blood cell involved in the body's immune response. This contrasts with other types of infections, such as bacterial meningitis, which often yields a neutrophilic predominance due to the characteristically higher cellular response to bacterial pathogens. Understanding CSF findings is crucial for diagnosing RMSF, particularly since the disease can mimic other febrile illnesses and present with neurological complications. The predominance of lymphocytes provides insight into the nature of the infection and aids in distinguishing RMSF from other forms of meningitis or encephalitis.