HEMOLYTIC UREMIC SYNDROME
DEFINITION:
A systemic disease characterized by the triad of microangiopathic
pathic hemolytic anemia, thrombocytopenia, and acute renal failure.
EPIDEMIOLOGY:
- incidence: 1-3/100,000
- age of onset:
- most common under the age of 4 years
- most common cause of acute renal failure in children
- risk factors:
- M = F
- highest incidence in summer and fall
TYPES:
- prodrome - diarrhea associated
- usually affects children 3 months -> 6 years (80% <3 years)
- E. coli serotype 0157:H7 can produce specific
enterocytotoxins:
- 100% DNA homology to shiga-like toxin-1 (SLT-1)
2. Verotoxin-2 (VT-2)
- 50-60% DNA homology to SLT-2
- these protein synthesis-inhibiting toxins adhere to
the intestinal epithelium and are then elaborated into
circulating cytotoxins
- endothelial cells are targetted by these cytotoxins
producing endothelial cell injury which:
- releases vWF multimers from damaged endothelial
cells which aggregate platelets (intrarenal) ->
thrombocytopenia
- decreases prostacyclin synthesis which interferes
with endothelial repair mechanisms
- microangiopathic anemia results from mechanical damage
to RBC's as they pass through altered vasculature
- risk factors for E. coli acquisition: undercooked
ground beef, contact with a person with diarrhea within 2
weeks prior to disease onset
- 1 in 10 children who have E. coli 0157:H7 will go on
to develop HUS
2. Atypical or Sporadic Form
- prodrome - none
- Classification:
- Pre-eclampsia
- Post Partum Renal Failure
5. Chemotherapy associated
CLINICAL FEATURES:
- usually precedes illness by 5-10 days
- diarrhea +/- bloody stool -> severe colitis
- fever, nausea and vomiting
- rectal prolapse
2. Renal Manifestations
2. Proteinuria
- can progress to the nephrotic level
3. Complications
- Nephritic Syndrome (edema, hypertension, azotemia,
oliguria)
- Nephrotic Syndrome (edema, hypoalbuminemia, hyperlipidemia)
- Renal Failure
- ranges from mild renal insufficiency to acute renal
failure (ARF)
3. Hematologic Manifestations
- sudden onset of pallor, irritability, lethargy, weakness
- hepatomegaly/hepatosplenomegaly
2. Thrombocytopenia (90%)
4. Complications
- irritability, seizures, coma
2. Gastrointestinal
- colitis with melena and perforation
3. Others
- acidosis, congestive heart failure, diabetes mellitus,
fluid overload, hyperkalemia, rhabdomyolysis
INVESTIGATIONS:
- HEMOLYTIC UREMIC SYNDROME, hemoglobinuria, proteinuria (minimal -> nephrotic)
- microscope - glomerular pattern - damaged RBC's and RBC
casts
2. Serum
- usually 50-90 g/L
- evidence of RBC hemolysis
- smear: burr cells, helmet cells, fragmented RBC's
- elevated plasma hemoglobin level
- decreased plasma haptoglobin level
- moderately elevated reticulocyte count
- negative Coombs test
2. Thrombocytopenia
3. Others
- leukocytosis (may rise to 30) with left shift
- normal PT, PTT, and fibrinogen
- acute renal failure (elevated BUN, creatinine, uric acid,
potassium, phosphate)
- decreased calcium, bicarbonate, albumin
3. Stool
- culture for E. coli serotype 0157:H7
MANAGEMENT:
- 90% survive the acute phase with no renal impairment if
aggressive management of acute renal failure (ARF) is instituted
2. Medical
- medical management of complications:
- diuretics, moniter fluids and electrolytes
2. Nephritic Syndrome
- fluid restriction, control hypertension, manage
hyperkalemia, manage pulmonary edema
3. Nephrotic Syndrome
- fluid restriction, salt-free diet, diuretics, albumin
transfusion, prednisone, alkylating agents
- see file on "Idiopathic Nephrotic Syndrome"
4. Chronic Renal Failure
- dialysis, kidney transplant
3. Prognosis
- mortality: 7-10%
- morbidity: 20% renal dysfunction from ARF
- young
- typical form
- summer months
2. Poor
- WBC >20
- shock
- significant renal involvement
- neurological signs and symptoms
- atypical form
INTERNET LINKS:
|