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Archimedes
Towards evidence based medicine for paediatricians Edited by Bob Phillips
QUESTION 1 Should a child with neurofibromatosis type 1 be screened for central nervous system tumours with neuroimaging? SCENARIO A 4-year-old boy with a recent diagnosis of neurofibromatosis type 1 (NF1) attends your outpatient clinic. His mother has read that optic pathway gliomas (OPG) occur in 15–20% of children with NF1 under 6 years of age. She is worried about the complications of this type of brain tumour, which include visual loss and precocious puberty. She asks you if her son can have an MRI scan to check for an optic pathway glioma. He has a normal ophthalmological examination.
QUESTION In a child with neurofibromatosis type 1 (NF1) ( patient), does screening for OPGs with MRI (intervention) compared to standard clinical examination and ophthalmological review (control) reduce the incidence of complications related to optic pathway glioma (outcome)?
SEARCH Cochrane—no relevant trials/reviews. Ovid Medline and EMBASE databases used. MeSH words used: Neurofibromatosis 1, Mass screening, optic chiasm, optic nerve glioma, optic nerve neoplasms, optic pathway glioma, magnetic resonance imaging. Keywords used: Neurofibromatosis type 1; MRI; Optic pathway glioma; Screening. Limited to English Language and Human. Medline search revealed eight results, of which four were potentially relevant. Embase search revealed 100 results, of which 11 were potentially relevant. Only one relevant study was found which examined the use of MRI screening for OPGs. This study, along with two studies examining the use of ophthalmological review to detect symptomatic OPGs, is summarised in the table below.
Non-random reflections on effectiveness There’s a (mistaken) belief that the only important things in EBM are randomised controlled trials (RCTs). This isn’t true,1 but RCTs are shockingly useful at showing where purported effects are likely to be real. But they aren’t always necessary: take the parachute argument2—do you need an RCT for parachutes (as there are survivors of non-’chuted falls)? The ‘mothers kiss’3 for nostrilly based crayons is another good example. (This is the use of the mother, or other fearless caregiver, to put their mouth against the unblocked nostril of their child and exhaling hard, to retrieve the drawing implement.) It works; so why do an RCT? Well, it’s not just that—it works, and it’s unlikely to cause harm, and it’s a situation where the crayon’s not coming out on its own —so why do an RCT? To frame it alternatively, “what biases would have to be present in these observational studies, and how large would these biases have to be, in order to invalidate the result?” If the answer to this question is “so large you wouldn’t believe it was possible”, then you don’t need an RCT. The smaller the proposed effect size, the greater the need for randomised trial data. As a rule of thumb, if the effect is a relative risk of >5 (or
Archimedes
Towards evidence based medicine for paediatricians Edited by Bob Phillips
QUESTION 1 Should a child with neurofibromatosis type 1 be screened for central nervous system tumours with neuroimaging? SCENARIO A 4-year-old boy with a recent diagnosis of neurofibromatosis type 1 (NF1) attends your outpatient clinic. His mother has read that optic pathway gliomas (OPG) occur in 15–20% of children with NF1 under 6 years of age. She is worried about the complications of this type of brain tumour, which include visual loss and precocious puberty. She asks you if her son can have an MRI scan to check for an optic pathway glioma. He has a normal ophthalmological examination.
QUESTION In a child with neurofibromatosis type 1 (NF1) ( patient), does screening for OPGs with MRI (intervention) compared to standard clinical examination and ophthalmological review (control) reduce the incidence of complications related to optic pathway glioma (outcome)?
SEARCH Cochrane—no relevant trials/reviews. Ovid Medline and EMBASE databases used. MeSH words used: Neurofibromatosis 1, Mass screening, optic chiasm, optic nerve glioma, optic nerve neoplasms, optic pathway glioma, magnetic resonance imaging. Keywords used: Neurofibromatosis type 1; MRI; Optic pathway glioma; Screening. Limited to English Language and Human. Medline search revealed eight results, of which four were potentially relevant. Embase search revealed 100 results, of which 11 were potentially relevant. Only one relevant study was found which examined the use of MRI screening for OPGs. This study, along with two studies examining the use of ophthalmological review to detect symptomatic OPGs, is summarised in the table below.
Non-random reflections on effectiveness There’s a (mistaken) belief that the only important things in EBM are randomised controlled trials (RCTs). This isn’t true,1 but RCTs are shockingly useful at showing where purported effects are likely to be real. But they aren’t always necessary: take the parachute argument2—do you need an RCT for parachutes (as there are survivors of non-’chuted falls)? The ‘mothers kiss’3 for nostrilly based crayons is another good example. (This is the use of the mother, or other fearless caregiver, to put their mouth against the unblocked nostril of their child and exhaling hard, to retrieve the drawing implement.) It works; so why do an RCT? Well, it’s not just that—it works, and it’s unlikely to cause harm, and it’s a situation where the crayon’s not coming out on its own —so why do an RCT? To frame it alternatively, “what biases would have to be present in these observational studies, and how large would these biases have to be, in order to invalidate the result?” If the answer to this question is “so large you wouldn’t believe it was possible”, then you don’t need an RCT. The smaller the proposed effect size, the greater the need for randomised trial data. As a rule of thumb, if the effect is a relative risk of >5 (or
