Rosen & Barkin's 5-Minute Emergency Medicine Consult (45 page)

• 298.9 Unspecified psychosis
  
• 780.97 Altered mental status
  

BASICS

• Invasive parasitic infection with both intestinal and extraintestinal manifestations
  
• Endemic worldwide, especially areas with poor sanitation
  
• Populations at risk:
  
  • Travelers to, citizens of, and immigrants from endemic areas
    
  • Institutionalized persons
    
  • Practitioners of oral–anal sexual activity
    
  • Men who have sex with men (MSM)
    
  • HIV infected individuals
    
• Risk factors for increased severity of disease and complications:
  
  • Immunocompromised: Corticosteroid use, HIV infection, malnutrition, malignancy
    
  • Pregnancy/postpartum state
    
  • Extremes of age
    

• Entamoeba histolytica,
  an anaerobic, nonflagellated protozoa
  
• Fecal–oral transmission:
  
  • Humans are sole reservoir.
    
• Ingested organisms cause invasive colitis.
  
• Extraintestinal spread is hematogenous.
  

DIAGNOSIS

• Intestinal disease:
  
  • Onset 1 wk to 1 mo postexposure
    
  • Acute diarrhea (nondysenteric colitis):
    
    • 80% of cases
      
    • Afebrile
      
    • Occult blood in stool
      
    • Benign abdominal exam
      
  • Classic dysentery:
    
    • Bloody mucoid diarrhea
      
    • Abdominal pain/benign abdominal exam
      
    • Tenesmus
      
    • Weight loss
      
    • Fever (rare)
      
  • Fulminant colitis:
    
    • Toxic-appearing patient
      
    • Rigid abdomen (25%)
      
    • Fever
      
    • Severe bloody diarrhea
      
    • Rapid progression to perforated bowel and frank peritonitis
      
    • >40% mortality
      
  • Toxic megacolon:
    
    • Toxic-appearing patient
      
    • Profuse diarrhea (>10 stools per day)
      
    • Fever
      
    • Distended, tympanitic abdomen with signs of peritonitis
      
    • Associated with corticosteroid use
      
    • High mortality
      
  • Ameboma:
    
    • Intraluminal granulated mass
      
    • Tender palpable mass on exam
      
  • Amebic strictures:
    
    • Owing to chronic inflammation/scarring
      
    • Crampy abdominal pain
      
    • Nausea and vomiting (may be feculent)
      
    • Partial or complete bowel obstruction
      
  • Chronic amebic colitis:
    
    • Mild recurrent episodes of bloody diarrhea, abdominal cramping, and tenesmus
      
    • Weight loss
      
    • May persist for years
      
• Extraintestinal disease:
  
  • Amebic liver abscess:
    
    • Most frequent extraintestinal manifestation (3–9% of cases)
      
    • Single abscess in right lobe (50–80%)
      
    • May develop months to years postexposure (median of 3 mo)
      
    • Fever
      
    • Right upper quadrant pain
      
    • Hepatomegaly with point tenderness
      
    • Rales at right lung base
      
    • Concurrent diarrhea unusual (20–33%)
      
    • Complication: Rupture into pleural cavity (10–20%), peritoneum, or pericardium (rare)
      
    • Increased risk of rupture if >5 cm in diameter or left lobe location
      
  • Extrahepatic amebic abscess:
    
    • Brain
      
    • Lung
      
    • Perinephric
      
    • Splenic
      
    • Vaginal/cervical/uterine
      
  • Cutaneous amebiasis:
    
    • Perineum and genitalia
      
    • Painful, irregularly shaped ulcers
      
    • Purulent exudate
      

Fulminant colitis is more likely

Fulminant colitis is more likely

• Possible sources of exposure
  
• Membership in high-risk group
  

• Identify evidence of peritonitis, sepsis, or shock.
  
• Tender abdominal mass mandates workup for liver abscess or ameboma.
  
• Digital rectal exam shows gross or occult blood in >70% of patients.
  

• CBC:
  
  • Leukocytosis in amebic liver abscess and peritonitis
    
• Alkaline phosphatase and ALT:
  
  • Elevated in amebic liver abscess
    
• Serum electrolytes, BUN/creatinine if prolonged diarrhea or evidence of dehydration
  
• Stool PCR is diagnostic gold standard:
  
  • 100% sensitive and specific
    
• Stool ELISA for
  E. histolytica
  –specific antigen:
  
  • 74–95% sensitive, 93–100% specific
    
• Serum for anti-
  E. histolytica
  antibodies:
  
  • Essential if suspecting liver abscess. These patients rarely shed parasites in stool
    
  • 90–100% sensitive in amebic liver abscess
    
  • 70–90% sensitive in amebic colitis
    
• Stool microscopy is <60% sensitive and no longer the test of choice.
  
• Fecal leukocytes and culture:
  
  • Rule out infection of enteroinvasive bacteria;
    
  • Negative in amebiasis
    

• Abdominal US:
  
  • 58–90% sensitive for liver abscess
    
  • Sensitivity influenced by size and location
    
  • Evaluate abscess for increased risk of rupture (>5 cm or located in left lobe)
    
• Abdominal CT or MRI:
  
  • Equivalent to US for delineating liver abscesses
    
  • Superior to US for detecting abscesses in other organs
    
• Head CT or MRI:
  
  • Suspect amebic brain abscess if patient with known amebiasis has altered mental status or focal neurologic findings.
    
  • Irregular nonenhancing lesions
    
• CXR:
  
  • Elevated right hemidiaphragm and/or right pleural effusion in liver abscess
    

• Colonoscopy with biopsy provides definitive diagnosis of amebic dysentery, colitis, ameboma, and amebic stricture.
  
• Percutaneous fine-needle aspiration of liver abscess to exclude bacterial abscess if nondiagnostic serology or antiamebic therapy fails
  
  • Not for primary treatment of liver abscesses
    

• Intestinal amebiasis:
  
  • Enteroinvasive bacterial infection (
    Staphylococcus, E. coli, Shigella, Salmonella, Yersinia, Campylobacter
    )
    
  • Inflammatory bowel disease
    
  • Ischemic colitis
    
  • Arteriovenous malformation
    
  • Abdominal aortic aneurysm
    
  • Perforated duodenal ulcer
    
  • Intussusception, diverticulitis
    
  • Pancreatitis
    
  • Colorectal carcinoma
    
• Amebic abscess:
  
  • Bacterial abscess
    
  • Tuberculous cavity
    
  • Echinococcal cyst
    
  • Malignancy
    
  • Cholecystitis
    
• Cutaneous amebiasis:
  
  • Carcinoma
    
  • STDs (condyloma acuminata, chancroid, syphilis)
    

TREATMENT

• Airway, breathing, circulation (ABCs)
  
• IV 0.9% NS if signs of significant shock
  

• Oral fluids if mild; IV if moderate/severe dehydration
  
• Avoid antidiarrheal agents.
  
• Correct serum electrolyte imbalances.
  
• Stool sample for
  E. histolytica
  PCR or ELISA, plus serology for anti–
  E. histolytica
  antibodies
  
• If stool or serum is positive for
  E. histolytica
  :
  
  • Metronidazole or tinidazole is 1st-line drug for systemic amebiasis (90% cure rate)
    
  • Chloroquine is an alternative systemic agent
    
  • Always follow systemic therapy with a luminal agent to eradicate intestinal colonization (erythromycin, iodoquinol, nitazoxanide, paromomycin, or tetracycline).
    
  • Do not use the luminal agents alone
    
• If stool or serum is negative for
  E. histolytica
  :
  
  • Refer to gastroenterologist for colonoscopy with biopsy.
    
  • Repeat serology in 7 days.
    
  • Consider empiric course of metronidazole if high suspicion for amebiasis and patient is critically ill.
    
• If evidence of peritonitis or sepsis:
  
  • Add IV antibiotic directed against anaerobic and gram-negative bacteria.
    
  • Surgery if toxic megacolon or perforation
    
• If liver abscess is suspected:
  
  • US or CT of hepatobiliary system with concurrent amebic serology
    
  • If imaging demonstrates an abscess but serology is negative, treat with amebicides and repeat serology in 7 days.
    
  • Consider abscess drainage by surgeon or interventional radiologist in conjunction with amebicidal therapy.
    
  • If symptoms do not improve after 5–7 days of empiric amebicidal therapy, consider fine-needle aspiration to rule out bacterial abscess or hepatoma.
    

• Use metronidazole with caution in 1st-trimester pregnancy, but do not withhold if patient has fulminant colitis or amebic abscess.
  
• Use erythromycin or nitazoxanide as intestinal amebicides along with metronidazole.
  
• Erythromycin or nitazoxanide may be used alone for mild dysentery in 1st-trimester pregnancy.
  
• Chloroquine, iodoquinol, paromomycin, tetracycline, and tinidazole are contraindicated.