haemolytic uraemic syndrome ( hus ) is a thrombotic microangiopathy characterized by coombs - negative haemolytic anaemia , thrombocytopenia and microvascular thrombosis , with many patients also experiencing acute renal failure . approximately 90% of cases have typical hus , which is secondary to infection by a shiga - like toxin - producing escherichia coli . atypical hus ( ahus ) is a relatively rare non - shiga toxin - associated form of hus and accounts for the remaining 10% of cases . ahus is associated with dysregulation of the complement system , which causes chronic uncontrolled complement activation and leads to a pro - coagulant , platelet - activation state endothelial swelling and , ultimately , thrombotic microangiopathy [ 1 , 2 ] . in approximately 50% of ahus cases , mutations in genes encoding complement regulatory proteins [ e.g. membrane cofactor protein ( mcp ) ] ahus has a poor prognosis , with 50% of patients progressing to end - stage renal disease or dying within the first year of diagnosis , with a high risk of recurrence after kidney transplantation . patients with ahus do not always respond to plasma exchange . as ahus is linked to complement system dysregulation , inhibition of this system has been suggested as a rational therapeutic approach . eculizumab ( soliris ; alexion pharmaceuticals ) is a humanized monoclonal antibody that binds to the complement protein c5 , preventing cleavage of c5 to c5a and c5b , thereby inhibiting the generation of the terminal complement complex c5b-9a . eculizumab is approved for the treatment of paroxysmal nocturnal haemoglobinuria   and case reports indicate that eculizumab may also be beneficial in ahus [ 2 , 7 , 9 , 10 ] . a 44-year - old man was admitted to hospital with prolonged diarrhoea ( lasting 1 week ) , fever and anuria . on admission , blood analysis showed haemolytic anaemia : haemoglobin 6.9 g / dl , schistocytes in the blood smear , lactate dehydrogenase elevated to 1837 u / l and platelet count 111 000/dl . anti - nuclear , anti - phospholipid , anti - topoisomerase iii and anti - adamts-13 antibodies were negative . three weeks after being admitted , the patient still required haemodialysis despite receiving 4 u of fresh frozen plasma and initiating plasmaphaeresis . following 21 sessions of plasmaphaeresis , haemolysis , classical and alternative complement pathway analysis revealed normal plasmatic factor h ( 26 mg / ml , normal range 1256 ) , 70% plasmatic concentration of factor i ( normal range 71115 ) , without antibodies against factor h. the expression of mcp on leucocytes was 51% compared to control ( normal range 91109 ) and heterozygous mutation of intron 2 ( c.286 + 1g > c ) of the mcp gene . eculizumab was initiated 90 days after hospital admission at a dose of 900 mg weekly for 5 weeks , then 1200 mg every 2 weeks until week 27 . the patient received an anti - meningococcal vaccine 15 days prior to starting eculizumab . during eculizumab treatment , haemolysis was inhibited completely , thrombocytes and platelets returned to normal levels and diuresis increased slowly to 1.5 l / day . renal biopsy ( figure 1 ) conducted the second week after admission revealed occlusive thrombosis in several small- and medium - sized arteries with secondary ischaemic glomerular changes . there was extensive acute tubular necrosis in the renal tubules with focal areas of tubular atrophy . a second renal biopsy ( figure 2 ) performed 2.5 months after admission , and 3 weeks before starting eculizumab , showed changes similar to those observed at the first biopsy : thrombotic microangiopathic lesions persisted and there was deterioration of interstitial fibrosis and tubular atrophy . ahus is a rare and devastating disease linked to complement dysregulation and chronic uncontrolled complement activation . mcp mutations occur in 1015% of ahus patients and may be familial or sporadic with incomplete disease penetrance in families . ahus usually manifests in childhood , but sporadic cases have been reported that have variable onset and are often related to infections , drugs or other clinical situations that trigger complement activation . in the case reported here , the clinical disease onset seems to have a been triggered by an infection . patients with ahus , particularly those with mcp mutations , often have a poor response to plasmaphaeresis and/or fresh frozen plasma infusions [ 1 , 6 ] and require alternative or additional therapy . as an inhibitor of terminal complement activation , eculizumab may offer an effective treatment option . our patient presented with typical hus features , but a lack of response to plasmaphaeresis and no evidence of shiga toxin suggested ahus , although no family history of the disease was apparent . based on positive results from other cases [ 2 , 7 , 9 , 10 ] , we began eculizumab therapy 90 days post - admission . eculizumab was associated with inhibition of haemolysis and normalization of thrombocyte and platelet levels , allowing cessation of haemodialysis . unfortunately , renal function recovery was not possible with eculizumab in our patient . renal biopsy revealed that irreversible damage to the kidney had already been established by the time eculizumab was initiated . our case supports previous findings that initiation of eculizumab late in disease progression is unable to reverse pre - existing renal damage . early use of eculizumab in patients with ahus may prevent the thrombotic microangiopathy resulting from uncontrolled complement activation and could therefore help to avoid irreversible renal damage . indeed , eculizumab treatment has resulted in recovery of renal function in other ahus cases [ 7 , 10 ] . ahus caused by a mutation in the mcp gene has a good prognosis post - transplant , as the normal kidney corrects the defect and complement activation is maintained within the normal range . in conclusion , this case describes how eculizumab normalized the haematological parameters in a patient with ahus . probably due to the late initiation of treatment , eculizumab was unable to have an impact on the irreversible renal damage that had already occurred . consequently , we propose that early treatment initiation with eculizumab is warranted in patients with ahus in order to avoid irreversible renal damage .