In the latest Case Record of the Massachusetts General Hospital, a 59-year-old man was admitted to the hospital because of fever, confusion, rash, thrombocytopenia, and renal failure, 10 days after a hunting trip in the Nevada valley.
The combination of suspected infection, vasculopathy of small or medium-size vessels, thrombocytopenia, myositis, myocarditis, encephalitis, and possible tick exposure is a classic constellation for a tickborne rickettsial disease such as Rocky Mountain spotted fever. Patients with other tickborne diseases, such as human monocytic ehrlichiosis and human granulocytic anaplasmosis, typically present with leukopenia, and rash is uncommon.
- What is the typical presentation of Rocky Mountain spotted fever?
Rickettsia rickettsii, the causative organism for Rocky Mountain spotted fever, has a tropism for endothelial cells. Findings include a maculopapular rash that begins peripherally, often involving the palms and the soles, followed by central spreading. Small-vessel vasculitis leads to hemorrhage from small blood vessels into the skin, a phenomenon manifested by petechial or purpuric lesions. The small-vessel vasculitis in Rocky Mountain spotted fever typically has multisystem involvement and has been associated with myocarditis, myositis, and encephalitis. Adhesion of platelets to injured endothelium leads to the thrombocytopenia classically associated with Rocky Mountain spotted fever. Headache as a presenting symptom is second in frequency to fever in adults with Rocky Mountain spotted fever. The incubation period for Rocky Mountain spotted fever is 5 to 10 days. Despite its name, Rocky Mountain spotted fever is most common in the southeastern and south-central United States.
- What is septic vasculopathy?
Septic vasculopathy is associated with a variety of infections and can be caused by several mechanisms, including direct invasion of endothelial cells by microorganisms, immune-mediated processes, and septic embolic phenomena. Rocky Mountain spotted fever is the prototype for direct endothelial invasion. Meningococcal disease is the prototype for immune-mediated small-vessel vasculitis, which results from immune-complex formation, complement activation, and endotoxin effects. Although meningococcal disease can affect all age groups, severe disease is more common in children and young adults, and this patient’s deteriorating condition over a period of several days was slower than the typically rapid decompensation over a period of hours in patients with meningococcal meningitis. Infective endocarditis is the prototype for septic embolic vasculitis, although infective endocarditis can also cause septic vasculopathy through immune-complex formation.
Morning Report Questions
Q: What percentage of patients with infective endocarditis do not have a known cardiac condition?
A: Although we typically think of infective endocarditis as occurring in persons with underlying heart disease, nearly 25% of patients with this disorder do not have any predisposing condition, such as a prosthetic valve or structural heart disease. Furthermore, in nearly 30% of patients with infective endocarditis, a new or worsened murmur cannot be documented on examination.
Q: What are characteristic cutaneous manifestations of infective endocarditis?
A: Janeway’s lesions, frequently found on the palms or soles, are a vascular phenomenon that produces painless spots thought to represent microabscesses from septic emboli. Osler’s nodes, often found on the fingers or toes, are an immunologic phenomenon that produces painful nodules thought to be caused by immune-complex-mediated vasculitis. Petechiae and splinter hemorrhages are also commonly seen in infective endocarditis. Petechiae are the most common dermatologic manifestation and may be seen on skin or mucous membranes.