Abstract
We report a case of ARDS complicating a case of typical post diarrhoeal haemolytic uraemic syndrome (HUS) with acute renal failure in a six month old female. This is a rare and potentially fatal complication. Our patient succumbed to the pulmonary and renal failure.

Introduction

The term haemolytic uraemic syndrome (HUS) was first used by Gasser et al in 1955, to describe the association of acute intravascular haemolytic anaemia and renal failure in infants and young children.1 The defining features of HUS are renal microangiopathy, microangiopathic haemolytic anaemia and platelet destruction leading to thrombocytopenia HUS has been classified as epidemic (prodromal) or sporadic (non-prodromal or atypical). The epidemic form, more common in children is associated with an enteritis prodrome caused by Verotoxin producing E-coli (VTEC) and Shigellae dysenteriae and has a better prognosis, compared to the non prodromal form, commonly seen in adults, which is likely to relapse and may be associated with a family history. It has also been associated with number of drugs, cancers and transplantation.1 The kidney arterioles and glomerular capillaries are most commonly involved and the lung and liver arterioles are rarely involved.²

Clinical Summary

A six month old female presented with haematuria and proteinuria. Acute renal failure and respiratory distress, on admission. 15 days prior to admission the child had an episode of diarrhoea. X-ray chest was suggestive of pulmonary haemorrhage. The patient was put on a ventilator but succumbed. A lung and liver necropsy was done.

Pathological Findings
Microscopy -
Lung necropsy : Arterioles (Fig. 1) showed luminal narrowing due to endothelial cell proliferation, intimal myxoid fibroplasia, and fibrinoid necrosis. Arterioles (Fig. 2) also showed evidence of onion skinning. The alveoli showed evidence of haemorrhage and hyaline membranes suggestive of ARDS
(Fig. 1).
Liver necropsy : Unremarkable.

Fig.1 : Photomicrograph of lung necropsy showing arterioles with luminal narrowing due to endothelium cell proliferation, intimal myxoid fibrinoid necrosis. Alveoli should haemorrhage and hyaline membranes (H & E, x100).	Fig.1 : Photomicrograph of lung necropsy showing arterioles with onion skiinning appearance. Bronchial showing mucosal lining hyperplasia. (H & E, x100).

Discussion

HUS is characterized by an acute intravascular haemolytic anaemia and renal failure. It has been classified into the following forms.¹

1. Classic childhood prodromal, epidemic HUS (D +), associated with an enteritis prodrome, caused by Verotoxin producing E. coli (O157:H7serotype) or S. dysenteriae and has a good prognosis.
2. Adult non prodromal, sporadic form,(D -) not proceeded by enteritis, has a worse prognosis and a likelihood of relapse and is associated with drug intake, cancer and transplantation and may be associated with a family history.

The classic childhood prodromal HUS is rarely complicated with pulmonary haemorrhage and ARDS.^3,4 Our case was the classic childhood HUS, who had a history of an episode of diarrhoea, 15 days prior to the development of acute renal failure, with haematuria and respiratory distress due to ARDS.

The central features of HUS are vascular endothelium damage in the glomerular capillaries, renal arterioles and to a lesser extent, other vessels.^5,6 The injury is due to the direct consequence of verotoxins produced by E. Coli (VPEC) and Shigellae toxin (STx) produced by Shigellae dysenteriae. There is a subsequent activation and aggregation of platelets. There is a microangiopathic haemolytic anaemia and thrombocytopenia, in addition to haemoglobinaemia, lowered serum haptoglobin levels, raised bilirubin, blood urea and serum creatinine levels. Our patient had anaemia and thrombocytopenia.1

Microscopy of the blood vessels, shows narrowing of the lumen due to endothelial hyperplasia, intimal myxoid fibroplasia, fibrinoid necrosis and onion skinning. In our case, a lung and liver necropsy was done, but a kidney necropsy was not done. The lung arterioles showed the characteristic changes (Figs. 1, 2) which were not seen in the liver biopsy vessels. In addition there were histological changes of ARDS in the lungs (Fig. 1). The pulmonary vascular changes are rare in occurrence,^3,4 in fact both the lung and liver blood vessels have been cited as being rarely involved.²

The prognosis is favourable, if the renal failure is managed by dialysis and the respiratory failure by ventilator support, the patient recovers within weeks however our patient succumbed to the respiratory and renal failure.

References

*Associate Professor, **Professor and Head, ***Lecturer, +Resident Pathologist, Department of Pathology, Grant Medical College, Mumbai - 400 008.