Correspondence on “National reduction in cerebral arteriovenous malformation treatment correlated with increased rupture incidence” by Luther et al

It was with great interest that we read the paper by Luther et al reporting a decrease in intervention for unruptured brain arteriovenous malformations (AVMs) with a corresponding increase in the incidence of ruptured cerebral arteriovenous malformations after the publication of A Randomised trial of Unruptured Brain Arteriovenous malformations (ARUBA) in 2014. We commend the authors for their efforts to address an important clinical question using rigorous analytic methods. However, while the authors acknowledge the general limitations of administrative database studies, there are particular methodological limitations to studying brain AVMs and ARUBA via the Nationwide Inpatient Sample that bear mentioning—namely, the nonspecificity of AVM codes, and the transition from ICD9 (international classification of diseases, ninth revision) to ICD10 in the US immediately following the publication of ARUBA. First, AVM diagnosis codes are particularly nonspecific. In ICD9, cerebral AVMs were included in the code 747.81, ‘anomalies of the cerebrovascular system’. As Cloft discussed previously, a study of patients with this code found that only 66% had a cerebral AVM, while the others had cavernous malformations (13%), unruptured cerebral aneurysms (10%), dural arteriovenous fistulae (8%), and venous anomalies (2%). In ICD10, the detection of incident cerebral AVMs via codes Q28.2 (‘arteriovenous malformation of cerebral vessels’) and I60.8 (‘other nontraumatic subarachnoid hemorrhage’) was characterized by the Scottish Intracranial Vascular Malformation Study and compared with patient records, finding a sensitivity of 72% and a positive predictive value of only 46%. This degree of uncertainty in the diagnosis itself warrants consideration when the reported findings of absolute change before and after ARUBA were only 5.8% and 3.9% for intervention and rupture rates, respectively. Second, while ICD10 introduced the new, supposedly more specific, code Q28.2, ‘arteriovenous malformation of cerebral vessels’, the timing of the transition from ICD9 to ICD10 (October 2015 in the US) only 1 year after publication of ARUBA introduces another potential confounding factor when evaluating the effect of ARUBA via administrative data. In dealing with this transition, for consistency the authors also included the code Q28.3, ‘other malformations of cerebral vessels’ in their definition of AVMs under ICD10. While this combination of codes appears to be the most appropriate, equivalent to the previous single code 747.81, it likely remains similarly nonspecific. Furthermore, to our knowledge, it has not been validated in the context of other new codes, and the ways in which the sensitivity and specificity for AVM identification may have changed are unknown. Interestingly, the authors report an increase in the incidence of AVM rupture at or before 2013, prior to the publication of ARUBA. The decrease in intervention rate (which had been slowly declining over time) takes a sudden downtown after 2015. It is not evident that the decrease in interventions can be attributed directly to ARUBA alone; the potential impact of the introduction of ICD10 codes must also be considered. A separate analysis of only those with the (presumably) more specific code Q28.2 for rupture and intervention rates may provide further information. We suspect rates of both intervention and hemorrhage may differ substantially with this code alone, a phenomenon that may explain the findings of a similar study examining trends before and after ARUBA that used only Q28.2 for ICD10. Finally, while these methodological limitations deserve mention, we do not feel that they necessarily invalidate the results of the study. In fact, the persistence of a trend despite the potentially diluted pool of AVM diagnoses may indicate that the true trends are of greater magnitude than what Luther et al have observed. The nonspecific nature of both past and present codes complicates the study of this pathology, despite investigators’ best efforts to define a ‘clean’ pool of diagnoses. While claims studies may be our current best method for assessing overall trends, this highlights the need to develop and maintain registries that also include not only treated, but also untreated pathologies.