1. Hemolytic uremic syndrome
Is a disease primarily of infancy and early childhood.
It is characterized by the triad of microangiopathic hemolytic anemia, thrombocytopenia, and acute renal failure (uremia).
HUS is the most common cause of acute renal failure in children.

2. Etiology Infection induced
HUS often follows a prodromal infectious disease, usually diarrhea (90%) and less often an upper respiratory infection (10%).
Use of antimotility drugs may increase the risk of developing HUS.
In Europe the most common cause of HUS is a verotoxin-producing Escherichia coli serotype O157:H7.

3. In Asia Shiga toxin-producing Shigella dysentereriae type 1 more common
others include: Streptococcus pneumoniae
Human immunodeficiency virus
Genetic cause
Other diseases associated with microvascular injury
SLE, Antiphospholipid antibody syndrome, Following bone marrow transplantation, Malignant hypertension and ,Primary glomerulopathy.

4. Pathophysiology
Transmission of E coli O157:H7 appears to be caused by contaminated food.
Person-to-person contact, as well as contamination of public water supplies, may also have a role in the transmission of this bacterium.

5. Endothelial cell injury appears to be the primary event in the pathogenesis of HUS, this injury may result from toxins released by bacteria (verotoxin).
The endothelial damage triggers a cascade of events that result in microvascular lesions with platelet-fibrin hyaline microthrombi that occlude arterioles and capillaries.
The platelet aggregation results in a consumptive thrombocytopenia.

6. in HUS, microthrombi are essentially confined to the kidneys, Hence, renal involvement is the defining feature of HUS.
Evidence of DIC is lacking.
While in thrombotic thrombocytopenic purpura, the hyaline microthrombi occur throughout the microcirculation, and microvascular thromboses may be found in the brain, skin, intestines, skeletal muscle, pancreas, spleen, adrenals, and heart.

7. Clinical manifestations
HUS is typically observed in infants and children, especially those aged 6 months to 4 years.
HUS is reported less often in adults than in children.

8. Fever, vomiting, abdominal pain, diarrhea that is often bloody.
Sudden onset of pallor, , irritability, weakness, lethargy & oliguria usually occur 5-10 days after initial gastrointestinal illness.
Neurologic symptoms: Seizures may occur, in some cases secondary to the development of a hypertensive encephalopathy.

9. Physical examinations may reveal pallor, dehydration, edema, petechiae , purpura and hepatosplenomegaly.
Complications:
GI involvement may lead to symptoms of an acute abdomen, with occasional perforation.
Cardiac involvement may lead to congestive heart failure (CHF), pericarditis and arrhythmias.

10. 3. Microinfarcts in the pancreas may cause pancreatitis or, rarely, insulin-dependent diabetes mellitus.
4. Ocular involvement may lead to retinal or vitreous hemorrhage.
5. Other complications: skin necrosis, parotitis, adrenal dysfunction, & hypertension.

11. Diagnosis
HUS is primarily a clinical diagnosis coupled with consistent laboratory findings.
Hemoglobin typically less than 8 g/dL). This is the hallmark finding and is necessary to establish the diagnosis.

12. The peripheral smear show the presence of schistocytes
The peripheral smear show the presence of schistocytes. These consist of fragmented, deformed, irregular, or helmet-shaped RBCs, they reflect the fragmentation of RBCs
The reticulocyte count is elevated.
Thrombocytopenia is present, less than 60,000/mm³
Prothrombin time (PT), activated partial thromboplastin time (aPTT), and fibrinogen are normal, thus differentiating HUS/TTP from DIC.

13. Elevation of lactate dehydrogenase (LDH) and indirect bilirubin reflects intravascular hemolysis. The bilirubin rarely exceeds 2-3 mg/dL.
Haptoglobin is very low.

14. The coombs test is negative.
Leukocytes count may increase to 30,000/mm³
Blood urea nitrogen (BUN) and creatinine are markedly elevated.
Finding on urinalysis are mild & consist of low grade microscopic hematuria & proteinuria.

15. Differential diagnosis
SLE, malignant hypertension
Bilateral renal vein thrombosis (marked renal enlargement, absence of real vein flow by Doppler ultrasound).
Henoch-Schonlein purpura.
Thrombotic thrombocytopenic purpura.

16. Prognosis
With careful supportive care, for diarrhea-associated HUS has <5% mortality
Most recover renal function completely, but of surviving patients, 5% remain dependent on dialysis
20-30% are left with chronic renal insufficiency.

17. Treatment
Blood transfusion in case of anemia.
Correction of volume deficit
Control of hypertension
and early institution of dialysis if the patient becomes anuric or significantly oliguric.
PD controls the manifestations of uremic state, and also removes the inhibitors of fibrinolysis from the circulation.
Plasmapheresis or fresh frozen plasma transfusion is recommended but its benefit is still not proven.