A 62-year-old man is brought to the hospital due to altered mental status. He has had 4 days of headaches, fever, myalgia, and chills. Medical history is significant for hypertension and a transient ischemic attack. The patient takes aspirin, amlodipine, and simvastatin. He works as horse trainer on a farm in Texas. Temperature is 38.1 C (100.6 F), blood pressure is 108/68 mm Hg, and pulse is 98/min. On examination, the patient is drowsy. There is no neck stiffness. The lungs are clear to auscultation, and heart sounds are normal. No significant lymphadenopathy or hepatosplenomegaly is present. There is a petechial rash over the upper and lower extremities. Neurologic examination is nonfocal. Laboratory results are as follows:
| Complete blood count | |
| Hemoglobin | 13.5 g/dL |
| Platelets | 40,000/mm3 |
| Leukocytes | 4,500/mm3 |
| Serum chemistry | |
| Sodium | 129 mEq/L |
| Potassium | 4.2 mEq/L |
| Blood urea nitrogen | 30 mg/dL |
| Creatinine | 0.7 mg/dL |
What is the best next step in management?
Rocky Mountain spotted fever | |
Epidemiology |
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Clinical features |
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Laboratory findings |
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Diagnosis |
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Treatment |
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ALT = alanine transaminase; AST = aspartate transaminase. | |
This patient's constitutional symptoms, confusion, petechial rash, hyponatremia, and thrombocytopenia raise suspicion for Rocky Mountain spotted fever (RMSF), a tick-borne illness caused by Rickettsia rickettsii. Cases occur throughout the United States and are particularly common in those who spend time in grassy or wooded areas. Patients often do not recall the transmitting tick bite.
Manifestations begin with several days of viral-like nonspecific symptoms (eg, fever, chills, myalgia, and headache). Classic skin findings usually develop at day 3-5 of the illness; the hallmark lesion is a petechial rash that originates at the wrists and ankles, involves the palms and soles, and spreads to the arms, legs, and trunk. However, the rash may initially appear maculopapular and not include the palms and soles, which can confound the diagnosis. Supportive laboratory findings include thrombocytopenia due to intravascular platelet destruction and hyponatremia due to antidiuretic hormone release in response to hypovolemia from vascular injury. The white blood cell count is often normal, but leukopenia or leukocytosis can occur in some cases. Hepatic endothelial vascular injury often leads to transaminitis in advanced disease.
Because RMSF can quickly progress to multiorgan system damage and death, prompt empiric treatment with doxycycline is indicated. Serologic testing confirms the diagnosis.
(Choice A) Although bone marrow biopsy is sometimes required to diagnose thrombocytopenia when a noninvasive evaluation has been unrevealing, this invasive test would not be the best next step.
(Choice C) Severe symptomatic hyponatremia can cause confusion and is treated with hypertonic saline. However, symptomatic hyponatremia does not typically occur until the sodium level is <125 mEq/L. In addition, constitutional symptoms and thrombocytopenia make an alternate cause of confusion far more likely.
(Choice D) Plasmapheresis can be used to treat thrombotic thrombocytopenic purpura and hemolytic uremic syndrome. Both conditions are associated with thrombocytopenia, petechiae, and confusion; however, the thrombocytopenia is usually severe (eg, <10,000/mm3), and significant anemia is usually present due to microangiopathic hemolytic anemia.
(Choice E) Prednisone can treat immune thrombocytopenia, an acquired autoantibody disorder against platelets. However, patients usually have mild or moderate thrombocytopenia but are otherwise asymptomatic; the presence of hyponatremia, confusion, and constitutional symptoms make this unlikely.
Educational objective:
Rocky Mountain spotted fever is a tick-borne illness that presents with fever, headache, and a maculopapular or petechial rash on the wrists and ankles that spreads centrally. Thrombocytopenia and hyponatremia are characteristic laboratory findings. Prompt treatment with doxycycline decreases the risk of progressive disease and death.