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Renal Arcuate Vein Microthombi – A New Clinico-Pathological Entity Causing Acute Kidney Injury in Young Adults

Huda Mamoud1,Andrew Redfern1,Tom McCulloch2, Adam Shardlow1, Matthew Hall3, Catherine Byrne3, Nicholas M Selby1,4

1Department of Renal Medicine, Royal Derby Hospital,2Departments of Histopathology and3Renal Medicine, Nottingham University Hospitals,4Division of Medical Sciences and Graduate Entry Medicine, University of Nottingham

INTRODUCTION:Over the last three years, a series of patients have presented to neighbouring East Midlands renal units with a previously unrecognised clinico-pathological syndrome causing Acute Kidney Injury (AKI). The renal biopsy findings were distinctive and are not widely recognised as a cause of AKI. As we identified more cases, it became clear that there were unifying features in the clinical presentation that may differentiate this scenario from other more common aetiologies of AKI. We aim to describe the clinical history and renal biopsy findings of these cases, as well as describing the investigations that we have undertaken in an attempt to identify an underlying cause.

METHODS: Description of case series.

RESULTS:Clinical presentation: The index case in 2010 and a further four of the seven casespresented to one nephrology unit. The second two cases presented to a neighbouring nephrology unit. All cases were young adults (median age 24yrs, range 18-35yrs). Patients had AKI stage 2 or 3 without an obvious cause. Strikingly, all described marked loin or lower back pain; imaging in all cases was normal. Urinalysis was positive for blood in all cases and for protein in six (urine protein:creatinine ratio 19-123mg/mmol). All five cases that presented to same unit had consumed alcohol in moderate to large quantities within a few days of onset of symptoms (but all denied drug use). One of the cases presenting to the second unit occurred in the setting of a mixed overdose that included alcohol. Six patients underwent renal biopsy in view of the clinical picture or failure to initially respond to supportive therapy.

Histopathology: In each case the findings on biopsy were similar: well defined microthrombi in the renal arcuate veins associated with the presence of a stereotypical and unusual inflammatory reaction at the corticomedullary junction, in the absence of any other lesions to explain AKI.

Subsequent investigations:Six patients had mildly elevated CRP(median 47mg/dl, range 12-68). Immunology and microbiology screens were universally unremarkable, as were renal vein doppler and thrombophilia screen in the index case. In the most recent case, liquid chromatography mass spectrometry of urine did not detectany alcohols or recreational drugs including any of the 60+ known ‘designer drugs’. A ToxBase query did not reveal any other similar reports and a systematic review of the literature found only one previous description of similar histopathological changes, which occurred in the setting of ecstasy ingestion.

Outcome: All patients have had complete recovery of renal function, median number of days to a normal baseline creatinine was 17 days (range between 6-60 days) and none have had further episodes.

CONCLUSIONS: We describe a new clinico-pathological entity causing AKI in young adults, the cause for which is currently unclear. Awareness of this condition may help diagnosis in other cases, preventing unnecessary investigations and avoiding treatment for other conditions. Screening for recreational drug use should be considered in similar cases as well as storage of admission serum and urine samples. Planned next steps are a national survey of renal units to identify other potential cases, as well as a review of historical renal biopsy samples from patients of similar age who also sustained AKI.