Misunderstanding and Misuse of Basic Clinical Decision Principles among Child Abuse Pediatricians

The previous post about Dr. Cox, ensnared in a CPT (Child Protection Team) witch hunt in Wisconsin, has led me to evaluate several more research reports on child abuse, including SBS (shaken baby syndrome), AHT (abusive head trauma), and sentinel injuries.  These reports are rife with critical assumptions, severe limitations, and gross errors which greatly limit the resulting conclusions in most studies I have reviewed.  However, one study that was pointed out to me today  takes the cake.  I don't know what the prevalence of this degree of misunderstanding is, but CPTs and child abuse pediatricians need make sure they have a proper understanding of sensitivity, specificity, positive and negative predictive value, base rates, etc.  And they should not be testifying about the probability of child abuse at all if they don't have this stuff down cold. And I think this means that some proportion of them needs to go back to school or stop testifying.

The article and associated correspondence at issue is entitled The Positive Predictive Value of Rib Fractures as an Indicator of Nonaccidental Trauma in Children published in 2004.  The authors looked at a series of rib fractures in children at a single Trauma Center in Colorado during a six year period and identified all patients with a rib fracture.  They then restricted their analysis to children less than 3 years of age.  There were 316 rib fractures among just 62 children in the series; the average number of rib fractures per child is ~5.  The proper unit of analysis for a study looking at positive predictive value is children, sorted into those with and without abuse, and with and without rib fracture(s) as seen in the 2x2 tables below.

Pathologizing Lipid Laden Macrophages (LLMs) in Vaping Associated Lung Injury (VALI)

It's time to weigh in on an ongoing debate being waged in the correspondence pages of the NEJM.  To wit, what is the significance of lipid laden macrophages (LLMs) in VALI?  As we stated, quite clearly, in our original research letter,

"Although the pathophysiological significance of these lipid-laden macrophages and their relation to the cause of this syndrome are not yet known, we posit that they may be a useful marker of this disease.3-5 Further work is needed to characterize the sensitivity and specificity of lipid-laden macrophages for vaping-related lung injury, and at this stage they cannot be used to confirm or exclude this syndrome. However, when vaping-related lung injury is suspected and infectious causes have been excluded, the presence of lipid-laden macrophages in BAL fluid may suggest vaping-related lung injury as a provisional diagnosis."

There, we outlined the two questions about their significance:  1.) any relation to the pathogenesis of the syndrome; and 2.) whether, after characterizing their sensitivity and specificity, they can be used in diagnosis.  I am not a lung biologist, so I will ignore the first question and focus on the second, where I actually do know a thing or two.

We still do not know the sensitivity or specificity of LLMs for VALI, but we can make some wagers based on what we do know.  First, regarding sensitivity.  In our ongoing registry at the University of Utah, we have over 30 patients with "confirmed" VALI (if you dont' have a gold standard, how do you "confirm" anything?), and to date all but one patient had LLMs in excess of 20% on BAL.  For the first several months we bronched everybody.  So, in terms of BAL and LLMs, I'm guessing we have the most extensive and consistent experience.  Our sensitivity therefore is over 95%.  In the Layden et al WI/IL series in NEJM, there were 7 BAL samples and all 7 had "lipid Layden macrophages" (that was a pun).  In another Utah series, Blagev et al reported that 8 of 9 samples tested showed LLMs.  Combining those data (ours are not yet published, but soon will be) we can state the following:  "Given the presence of VALI, the probability of LLM on Oil Red O staining (OROS) is 96%."  You may recognize that as a statement of sensitivity.  It is unusual to not find LLMs on OROS of BAL fluid in cases of VALI, and because of that, their absence makes the case atypical, just as does the absence of THC vaping.  Some may go so far as to say their absence calls into question the diagnosis, and I am among them.  But don't read between the lines.  I did not say that bronchoscopy is indicated to look for them.  I simply said that their absence makes the case atypical and calls it into question.