Rosen & Barkin's 5-Minute Emergency Medicine Consult (236 page)

• Congestive Heart Failure
  
• Cor Pulmonale
  
• Deep Vein Thrombosis
  
• Angioedema
  
• Cirrhosis
  
• Venous Insufficiency
  
• Nephritic Syndrome
  
• Nephrotic Syndrome
  

CODES

• 782.3 Edema
  
• 992.7 Heat edema
  
• 995.1 Angioneurotic edema, not elsewhere classified
  

BASICS

• Tick-borne human infection presenting as a nonspecific febrile illness
  
• Several forms of ehrlichiosis exist; 2 predominate in North America
  
  • Human monocytic ehrlichiosis (HME), 1st described in 1987:
    
    • Vector tick:
      Amblyomma americanum
      (lone star tick)
      
    • Geographic range: Central, southern, and mid-Atlantic states, with range expanding to parts of New England
      
  • Human granulocytic ehrlichiosis or human granulocytic anaplasmosis (HGE or HGA), 1st described in 1994:
    
    • Vector tick:
      Ixodes scapularis
      (deer tick)
      
    • Geographic range: East Coast, mid-Central States, and Pacific Northwest (same areas as Lyme disease which is more common in US than HME)
      
• All are tick borne but have different vectors and geographic ranges. Other species have been reported, but at present HME and HGE are the important ehrlichial human pathogens.
  

• 2 distinct species of obligate intracellular organisms
  
• The taxonomy of these pathogens has changed in recent years as more DNA and ribosomal RNA data become available.
  
• HME is caused by the organism
  Ehrlichia chaffeensis.
  
• HGE/HGA is caused by
  Anaplasma phagocytophila
  (a new name as of 2002).
  
• The vasculitis found in Rocky Mountain spotted fever (RMSF) is usually not present.
  
• A 3rd type may also be encountered, caused by
  Ehrlichia ewingii,
  which has the tick vector of the lone star tick. Clinically similar to HME.
  
• Compared with RMSF, older individuals are usually affected, commonly >40 yr of age.
  

DIAGNOSIS

• Signs and symptoms of HME and HGE/HGA are similar.
  
• Many patients who are infected undergo asymptomatic seroconversion.
  
• The spectrum reported may overrepresent the more severely affected patients.
  
• With any tick-borne infection, patients can be coinfected by more than 1 pathogen from the same tick bite:
  
  • May have a complicated presentation of 2 different diseases
    
• 1/4 of children have severe disease.
  

• The season and other epidemiologic factors are important in diagnosing tick-borne diseases:
  
  • Most commonly present from April to October
    
  • Variability is likely owing to changes in weather patterns from year to year and from region to region.
    
• Symptom onset from 1–2 wk (median 9–10 days) following the tick bite:
  
  • Bite of the larger lone star tick is more likely to be recalled by the patient than that of the smaller deer tick.
    
• Abrupt onset of:
  
  • Fever
    
  • Chills
    
  • Headache
    
  • Myalgias
    
  • Malaise
    
• Rash:
  
  • HME (35–60% of cases)
    
  • HGE or HGA (∼5–10% of cases)
    
  • Often delayed and may be variable
    
• Symptoms may relate to complications of ehrlichiosis, such as:
  
  • ARDS
    
  • Renal failure
    
  • Hypotension and shock
    
  • Rhabdomyolysis
    
  • GI disturbances
    
  • CNS or peripheral nervous system (PNS) involvement, such as encephalopathy and meningitis as well as seizures
    
  • DIC
    
  • Immunocompromised patients have more severe complications.
    

• Fever
  
• Rash:
  
  • May be macular, maculopapular, or petechial
    
  • May be absent during 1st wk of illness
    
  • Usually involves trunk and spares hands and feet
    
• Lymphadenopathy
  
• Hepatosplenomegaly
  
• Neurologic findings:
  
  • Abnormal mental status
    
  • Meningismus
    
  • Nystagmus
    
• Pulmonary findings (rales, rhonchi) depending on pulmonary complications
  

• Fever, headache, and rash present in 48%
  
• Lymphadenopathy in 45%
  

• CBC:
  
  • Leukopenia
    
  • Thrombocytopenia
    
  • Anemia
    
• Hepatic transaminases:
  
  • Often elevated 2–6 times normal
    
• Indirect immunofluorescence antibody test, specific for HME and HGA
  
  • Usual test available
    
  • Threshold for a positive test is usually made by the individual lab testing the serum.
    
  • 94–99% sensitive when 2nd sample obtained over 14 days from onset of illness
    
• Wright stain of peripheral blood:
  
  • Morula may be seen:
    
    • Small intracytoplasmic ehrlichial DNA inclusion bodies
      
    • Diagnostic
      
    • Sensitivity of seeing morulae depend on who is looking, for how long, and the immunologic competence of the patient.
      
    • Found more commonly in HGE/HGA (∼50%) than in HME (∼10–15%)
      
• Culture and PCR for HEM and HGA
  
  • Not routinely available
    
• Antibody titer tests:
  
  • Not available in real time
    
• Lumbar puncture
  
  • Pleocytosis with predominance of lymphocytes and increased total protein
    

• Head CT for encephalopathy
  
• CXR for fever/dyspnea
  

• Most tick-borne illnesses:
  
  • RMSF
    
  • Lyme disease
    
  • Babesiosis
    
• Many viral and bacterial infections and numerous other infectious diseases, especially early in their course, can initially present with an undifferentiated febrile illness similar to ehrlichiosis.
  
• Mononucleosis
  
• Thrombotic thrombocytopenia purpura
  
• Hematologic malignancy
  
• Cholangitis
  
• Pneumonia
  

TREATMENT

ABCs

• Initiate antibiotics:
  
  • Doxycycline:
    
    • Drug of choice
      
    • Children who are affected should also receive doxycycline. 14 days of treatment does notappear to cause significant discoloration of permanent teeth. The risks and benefits in children <9 yr old should be specifically discussed with parents.
      
    • Treatment should be continued for at least 3 days past defervescence for a min. total course of 7 days. Severe or complicated disease requires a longer course.
      
  • Rifampin for:
    
    • Pregnant patients
      
    • Allergy to doxycycline
      
    • Mildly affected children <9 yr of age
      
    • Patients who are pregnant, allergic to doxycycline, or mildly affected can be given rifampin for 7–10 days.
      
• Initiate therapy for other tick-borne diseases that may have been cotransmitted.
  

Doxycycline:

• Adults: 100 mg IV/PO q12h for 10 days or for 3–5 days after defervescence.
  
• Children (severely affected): 4 mg/kg q12h IV/PO up to max. of adult dose; older children can be dosed as adult.
  

Despite the fact that doxycycline is generally contraindicated in patients <9 yr old, it is the drug of choice in young children who are severely affected by ehrlichiosis. In less affected children, rifampin has been used successfully.