**4. Comments**

HUS is a multisystemic entity; its incidence in Europe has been sporadic in the past, although recent migration movements have facilitated a relapse of cases in several countries. In general, older patients tend to show milder neurologic symptoms at onset, like drowsiness or irritability, while younger patients, especially under 18 months, tend to present seizures during the acute phase.

Physiopathology is not yet well understood, but experimental and in vivo studies (Ren et al., 1999; Carter, 1986; Cimolai, 1896) have proved that *Escherichia coli* VT induces thrombopenia through consuming, kidnapping, aggregation and platelet dysfunction mechanisms; plasminogen inhibitor activity is also enhanced, and therefore fibrinolysis is inhibited. Released factors such as TNF, IL, FvW monomers, free radicals, thromboxane, etc., provoke endothelial lesions and vasculitic events in several organs, especially kidneys, digestive system and brain (Seth et al., 1896; Miller & Kin, 1987; Montoliu, 1989; Hahn et al., 1989; Erikson et al., 2001; Steinborn et al., 2004; Rivero et al., 2004). VT receptors are present in various troncoencephalic nuclei, the amygdala and the hippocampus, and in the posterior root neurons of the ganglia. This suggests VT may induce primary neuronal damage as well as a vasculitic lesion (Hahn et al., 1989; Hamano et al., 1993; Rivero et al., 2004). This probably happens also at the basal ganglia, especially at putamen nucleae, the most frequent localization of CNS lesions (Nakamura et al., 2003). The vasculitic damage (due to the diffuse hypoxic-ischemic aggression) observed in our patients was mainly localized at cortico-subcortical areas and the basal ganglia, as described in previous reports (Ren et al., 1999; Akasaka et al., 1999; Garel et al., 2004). Clinical course of patients with these lesions was favorable, and MRI lesions became smaller on follow-up controls. Brain MRI sequenced controls of patients 6 and 21 reinforce the hypothesis of vasculitic lesion as the main cause of tissue damage, although direct neuronal toxicity could not be disclosed (Hahn et al., 1989). In contrast with previous reports (Theobald et al., 2001), basal ganglia necrosis has not proved to be a bad prognosis factor in our series: our patients did not present extrapyramidal signs, as other authors have reported (Di Mario et al., 1987; Barnett et al., 1995).

Unfavorable neurologic outcome was formerly correlated with seizures at onset of symptoms and plasmapheresis (unnecessary for our patients) at diagnosis (Cimolai et al.,

Five of the 25 patients with neurologic symptoms at the acute phase showed one or more medium-term neurological deficits (Table 3): 1/5 hemiparesia, 4/5 mild cognitive dysfunction and 2/5 visuo-perception and construction deficits, which almost normalized during long-term follow up. Nineteen of the 25 presented normal neurological examination

Patient 4 died within the first 15 hours after admission, after a rapidly progressive neurologic deterioration and respiratory arrest. He presented lower limb myoclonias after life rescue. Thorax x-ray revealed right inferior lobe (RIL) pneumonia. Abdomen and transfontanellar US were normal. Pathology studies confirmed RIL pneumonia, severe segmentary glomerular and tubular nephropathy, acute pancreatitis, lung and heart interstitial inflammation, diffuse alveolar damage, intracapillary thrombi in lungs and kidneys, brain cortical necrosis with edema and cerebellar granular necrosis. *Steptococcus pneumoniae* was not identified. This represents a mortality of 1.5% of the HUS patients and

HUS is a multisystemic entity; its incidence in Europe has been sporadic in the past, although recent migration movements have facilitated a relapse of cases in several countries. In general, older patients tend to show milder neurologic symptoms at onset, like drowsiness or irritability, while younger patients, especially under 18 months, tend to

Physiopathology is not yet well understood, but experimental and in vivo studies (Ren et al., 1999; Carter, 1986; Cimolai, 1896) have proved that *Escherichia coli* VT induces thrombopenia through consuming, kidnapping, aggregation and platelet dysfunction mechanisms; plasminogen inhibitor activity is also enhanced, and therefore fibrinolysis is inhibited. Released factors such as TNF, IL, FvW monomers, free radicals, thromboxane, etc., provoke endothelial lesions and vasculitic events in several organs, especially kidneys, digestive system and brain (Seth et al., 1896; Miller & Kin, 1987; Montoliu, 1989; Hahn et al., 1989; Erikson et al., 2001; Steinborn et al., 2004; Rivero et al., 2004). VT receptors are present in various troncoencephalic nuclei, the amygdala and the hippocampus, and in the posterior root neurons of the ganglia. This suggests VT may induce primary neuronal damage as well as a vasculitic lesion (Hahn et al., 1989; Hamano et al., 1993; Rivero et al., 2004). This probably happens also at the basal ganglia, especially at putamen nucleae, the most frequent localization of CNS lesions (Nakamura et al., 2003). The vasculitic damage (due to the diffuse hypoxic-ischemic aggression) observed in our patients was mainly localized at cortico-subcortical areas and the basal ganglia, as described in previous reports (Ren et al., 1999; Akasaka et al., 1999; Garel et al., 2004). Clinical course of patients with these lesions was favorable, and MRI lesions became smaller on follow-up controls. Brain MRI sequenced controls of patients 6 and 21 reinforce the hypothesis of vasculitic lesion as the main cause of tissue damage, although direct neuronal toxicity could not be disclosed (Hahn et al., 1989). In contrast with previous reports (Theobald et al., 2001), basal ganglia necrosis has not proved to be a bad prognosis factor in our series: our patients did not present extrapyramidal signs, as other authors have reported (Di Mario et al., 1987; Barnett et al.,

Unfavorable neurologic outcome was formerly correlated with seizures at onset of symptoms and plasmapheresis (unnecessary for our patients) at diagnosis (Cimolai et al.,

at hospital discharge, and one year later.

present seizures during the acute phase.

**4. Comments** 

1995).

4% of the patients with HUS and neurologic symptoms at onset.

1986). The nine patients who presented seizures at onset survived without long-term sequelae, whereas the only exitus presented initial drowsiness and rapidly progressive neurologic deterioration, without seizures (myoclonias happened after resuscitation maneuvers). This was the only patient with neurologic symptoms, acute pancreatitis, endocarditis and RIL pneumonia; *Streptococcus pneumoniae* was not detected (De Loos et al., 2002; Prestidge & Wong, 2009). Neurologic evaluation and follow-up of patients with CNS symptoms allowed early detection of subtle vision dysfunction, visual perception deficit, and mild cognitive disabilities.

Incidence of neurologic symptoms in acute phase of HUS in this group (39%) was similar to former descriptive studies (Sheth et al., 1986; Hahn et al., 1989; Garel et al., 2004; Steinborn et al., 2004); orolingual dystonia was previously observed, but cortical blindness, hallucinations (Cimolai et al., 1896) and cerebellar mutism/anarthria (Mewasingh et al., 2003) were not observed in our group. A slightly higher prevalence in girls was identified (boy/girl rate 1:1.2), as reported by other authors (Cimolai et al., 1986; Rivero et al., 2004; Zambrano et al., 2005); this rate is increased to 1:1,7 when regarding the neurologic patients, perhaps related to specific auto-immune characteristics.

It was previously reported that HUS patients with partial seizures tend to present epilepsy or abnormal movements after HUS recovery (Dhuna et al., 1992; Hue et al., 1992; Koehl et al., 2010). However, none of our patients developed abnormal movements during mediumand long-term follow-up, and seizures or EEG abnormalities at the acute phase did not determine a poor outcome (only the patient with previously diagnosed cortical dysplasia presented focal seizures).

SHU mortality has decreased in recent years, from 25% in the 1980s to 2% in more recent publications (Rivero et al., 2004). Despite this low mortality rate, a small percentage of patients with neurological symptoms at the acute stage subsequently present neurological sequelae. In our series of 25 children with neurological symptoms, one patient died and 5 had medium-term neurological complications (hemiparesia, cognitive delay or visual perception deficit). The rates of medium-term neurologic morbidity (20%) and mortality (4%) were similar to those of other authors (Hahn et al., 1989; Erikson et al., 2001). Only in one patient after 3 years of follow-up were there persistent minor neurological sequelae (slight cognitive, visual perception and visual construction impairments), with gradual improvement despite the absence of significant changes on MRI and visual evoked potentials monitoring. Although neurocognitive impairment is not frequently reported in HUS (Roche et al., 2008), neuropsychological evaluation and follow-up of these children, especially when basal ganglia (mainly putamen) and cortico-subcortical regions are damaged at the initial brain MRI, helps to identify neurocognitive disabilities. Even if they are not severe, a good neurofunctional diagnosis and rehabilitation can help patients with their school performance and day-to-day life.
