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Numata et al.1 have conducted a retrospective study in a large sample of children born at term with spastic diplegia (i.e. bilateral leg-dominated spastic cerebral palsy [BSCP]), in which they investigated associations between neuroimaging findings, motor function, epilepsy, and cognitive function. They found no abnormalities on magnetic resonance imaging (MRI) in a surprisingly high percentage (of patients 41.9%), which is slightly higher than in previous studies on BSCP. In those patients with abnormalities a wide spectrum of lesions was seen, consistent with previous studies.2 Interestingly, the authors found that severity of motor and cognitive impairment did not differ significantly between those with normal and those with abnormal MRI. However, a smaller percentage of patients with normal MRI had epilepsy compared with those with imaging abnormalities. The authors concluded that in the large proportion of patients born at term with BSCP and normal MRI, genetic investigations and examination of early prenatal factors may contribute to understanding of the pathophysiology of CP.

A recent large population-based study in Canada3 did show normal MRI or unspecific findings in 29% of the patients and, consistent with other studies, that this was associated mainly with dyskinetic and ataxic CP. In this Canadian study, a large number of antenatal, perinatal, and neonatal variables were examined and no significant difference was found between those with normal and those with abnormal MRI. Both the study by Numata et al.1 and Benini et al.3 conclude that genetic and metabolic screening may be indicated in patients with normal MRI. Indeed, although not based on strong evidence, the recommendation of the American Academy of Neurology is to consider genetic and metabolic investigations in patients with CP and normal imaging findings.4

The study by Numata et al. is of interest since it is based on a large sample (n=86) of patients, focuses on term-born patients and on one CP type (BSCP), and includes information on severity of motor impairment and cognitive function, as well as epilepsy. However, it also highlights a number of issues that are common in studies on the pathophysiology of CP and associations between possible underlying brain lesions, severity of motor impairment, and cognitive function – all of which often make interpretation of findings and inferring conclusions difficult. In this study there was a large range with regards to age at diagnosis of CP, including patients who had been given the diagnosis of CP at an age (as young as 6mo) where one can still expect transitory neurological signs in a number of children, making a definite diagnosis of CP difficult. The study mainly used information obtained retrospectively from medical records with regards to type of CP, severity of motor impairment, and other relevant clinical variables. Some patients were scanned at an age as young as 10 months, when myelination is still not complete in typical development and which can make diagnosis of a non-progressive brain lesion difficult. In the light of the high proportion of normal MRI findings seen in this study, this emphasizes the importance of adhering to guidelines such as issued by the Surveillance of Cerebral Palsy in Europe Network (e.g. with regards to timing of CP diagnosis).

The study by Numata et al. also highlights that it is important to use advanced imaging techniques when investigating neuroanatomical correlates of CP, in particular in those cases where visual inspection of conventional MRI shows no abnormalities. Diffusion MRI is one such method that increases sensitivity in detecting abnormalities. For example, Son et al.5 have identified microstructural abnormalities in the cortico-spinal tract in patients with unilateral CP who had no abnormalities identified on visual inspection of conventional MRI.

It appears that future studies on this subject would benefit from using information from CP registers where the same diagnostic criteria and terminology are used and, importantly, information is collected according to standardized protocols. Common classification systems for neuroimaging findings and the use of advanced MRI should also be adopted. This will make comparison of findings across studies more reliable and increase the sensitivity of detecting subtle brain abnormalities, which might form the neural correlates of CP in a number of patients.

References

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  2. References
  • 1
    Numata Y, Onuma A, Kobayashi Y, et al.Brain magnetic resonance imaging and clinical analyses in 86 patients born at term with spastic diplegia. Dev Med Child Neurol. DOI: 10.1111/j.1469-8749. (Published online).
  • 2
    Krägeloh-Mann I, Horber V. The role of magnetic resonance imaging in elucidating the pathogenesis of cerebral palsy: a systematic review. Dev Med Child Neurol2007; 49: 14451.
  • 3
    Benini R, Dagenais L, Shevell MI, Registre de la Paralysie Cérébrale au Québec (Quebec Cerebral Palsy Registry) Consortium. Normal imaging in patients with cerebral palsy: what does it tell us?J Pediatr2012; [Epub ahead of print].
  • 4
    Ashwal S, Russman BS, Blasco PA, et al.Practice parameter: diagnostic assessment of the child with cerebral palsy: report of the Quality Standards Subcommittee of the American Academy of Neurology and the Practice Committee of the Child Neurology Society. Neurology2004; 62: 85163.
  • 5
    Son SM, Ahn YH, Sakong J, et al.Diffusion tensor imaging demonstrates focal lesions of the corticospinal tract in hemiparetic patients with cerebral palsy. Neurosci Lett2007; 420: 348.