Pediatric patients have a higher disease burden and activity on brain mri at time of ms onset than adults



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Pediatric patients have a higher disease burden and activity on brain MRI at time of MS onset than adults
E. Waubant,* D. Chabas,* D.T. Okuda,** O. Glenn,*** E.M. Mowry,** R. Henry,*** J. Strober,* B. Soares,*** M. Wintermark,*** D. Pelletier**
*UCSF Regional Pediatric Multiple Sclerosis Center, San Francisco, CA

**UCSF Adult Multiple Sclerosis Center, San Francisco, CA

***Department of Radiology, UCSF, San Francisco, CA
Title count: 87 characters

Body text count: 2179 words

Key words: multiple sclerosis onset, pediatric, adult, MRI
Corresponding author:

Emmanuelle Waubant, MD PhD

UCSF Regional Pediatric Multiple Sclerosis Center

350 Parnassus Ave., Suite 908

San Francisco, CA 94117

Tel: (415) 514-2468

Fax: (415) 514-2470

E-mail: Emmanuelle.waubant@ucsf.edu

Disclosure: The authors report no conflicts of interest.

EM conducted the statistical analysis

OBJECTIVE:

To compare initial brain MRI characteristics of children and adults at multiple sclerosis (MS) onset.


DESIGN:

Retrospective analysis of features of first brain MRI available at MS onset in pediatric-onset (PO) and adult-onset (AO) MS patients.


SUBJECTS:

We evaluated initial and second (when available) brain MRI scans of PO (under age 18) and AO (18 and above) MS patients obtained at the time of their first MS symptoms for lesions that were T2-bright, ovoid and well-defined, large (>1cm), or enhancing.


RESULTS:

We identified 41 PO and 35 AO MS patients. Children had a higher number of total T2- (median 21 vs 6, p<0.0001) and large T2-bright areas (median 4 vs 0, p<0.0001) than adults. Children more frequently had T2-bright foci in the posterior fossa (68.3% vs 31.4%, p=0.001) and enhancing lesions (68.4% vs 21.2%, p=0.0001) than adults. On the second brain MRI, children had more new T2-bright (median 2.5 vs 0, p<0.0001) and enhancing foci (p=0.0001) than adults. Except for corpus callosum involvement, race/ethnicity was not strongly associated with disease burden or lesion location on the first scan, although other associations cannot be excluded due to the width of the confidence intervals.

CONCLUSIONS:

While it is unknown whether the higher disease burden, posterior fossa involvement and rate of new lesions in POMS are explained by age alone, these characteristics have been associated with worse disability progression in adults.

Introduction

Multiple sclerosis (MS) onset before the age of 18 occurs in up to 10% of all MS cases.1 The lower incidence of MS in childhood contributes to decreased awareness and delayed diagnosis. Other factors that delay diagnosis in children include the different clinical phenotype at disease presentation in pediatric-onset (PO) MS compared to adult-onset (AO) MS.2

While it is possible that the MRI phenotype in children with POMS might also contribute to delayed diagnosis, the MRI characteristics that define MS in this age group are unclear. One report has suggested that pediatric patients with clinically definite MS may less often meet McDonald criteria for dissemination in space on initial brain imaging.3,4 Up to 40% of POMS patients may have tumefactive, T2-bright lesions defined as > 2 cm in diameter on their initial scan.5,6 Although pediatric patients with MS onset before 11 years have similar numbers of T2-bright foci on their initial brain MRI scan than patients with an onset between 11 and 18, these lesions tend to be less often ovoid and well-defined, and resolve more frequently at follow-up in the under-11 age group.7 This suggests the possibility of different underlying biological mechanisms at play in younger patients. Finally, pediatric patients with an initial demyelinating event, including first MS event, acute demyelinating encephalomyelitis (ADEM) and possibly other demyelinating disorders such as neuromyelitis optica (NMO) and complete acute transverse myelitis (ATM) may have a greater infratentorial lesion volume than adults with relapsing remitting (RR) MS.8 However, these reports have not compared MRI features in children vs. adults seen at the same initial stage of the disease.

We sought to determine if quantitative differences exist on brain MRI scans obtained at MS onset between children and adults. More specifically, as children more frequently have clinical brainstem/cerebellar involvement at MS onset than adults,2 we hypothesized that infratentorial involvement on the initial brain MRI would be more prominent in children at disease onset.


Methods

Pediatric patients

We queried the UCSF Pediatric MS database for patients with disease onset before 18 years of age who were diagnosed with MS or clinically isolated syndrome (CIS) according to recently published operational definitions.4,9,10 Patients with ADEM, NMO, recurrent optic neuritis with normal CSF and normal brain and spinal MRI scans, or complete ATM were excluded. Participation in the study was restricted to patients with an initial brain MRI scan obtained within three months of symptom onset before IV steroid therapy and initiation of disease modifying therapy (DMT). The clinical disease course of most of these patients (31 of 41) has been described elsewhere.7 MRI scans were performed in various facilities but were stored on the UCSF computerized PACS system. All patients had axial or coronal T2-FLAIR images available for review. Follow-up MRI scans consisted of the first repeat scans obtained after the first event available in the UCSF PACS system. All MRI scans were performed at a magnet field strength of 1.5 Tesla (1.5 T) except for two follow-up scans performed at 3 T which showed nearly complete resolution of the previously observed T2-bright foci. Only 8 of 41 first scans and 7 of 40 second scans were performed with overlapping slices on T2-FLAIR sequences. The scans performed with non-overlapping slices had a gap between slices of no more than 2 mm.



Adult patients

Adult CIS patients seen at UCSF MS center were part of a natural history study;11 entry criteria included at least two T2-bright foci in the deep white matter on a clinical brain MRI scan, age 18 or older, no exposure to IV steroid therapy for at least one month and no DMT at the time of baseline scan. Brain MRI scans were obtained using a standardized protocol at baseline and every three months during the first year. All brain MRI images were acquired on a 1.5 T GE scanner (General Electric Medical Systems, Milwaukee, WI) using a quadrature head coil. Each MR imaging examination included an axial T1-weighted three dimensional spoiled gradient echo (3D SPGR) imaging sequence (TE/TR = 6/27 ms, flip angle = 40, 192x256x124 matrix, 180 mm x 240 mm x 186 mm FOV) and slice thickness of 1.5 mm (with pixel resolution of 0.94x0.94x1.5 mm) and axial T2-weighted spin-echo images (TE/TR =80/2500 ms, 192x256 matrix, 180x240 mm FOV, 3 mm thick slices, no gap, 47 slices). Study scans obtained approximately six months after study entry were used for follow-up evaluation. The closest available scan was used when the scan at month 6 was not performed.



MRI reading:

All scans were independently and blindly reviewed. For both groups, the overall number of T2-bright lesions (defined as foci >3 mm2 of increased signal on the T2-FLAIR or T2-weighted spin-echo images), the number of well-defined ovoid and large (>1 cm) lesions, and the number of gadolinium-enhancing (Gd+) lesions were compared between the two age groups. Operational definitions were provided elsewhere.7 The number of Gd+ lesions was determined by comparing pre- and post-contrast T1-weighted sequences. All Gd+ lesions were also seen on T2-FLAIR or T2-weighted sequences. Areas of confluent T2-FLAIR hyperintensity, defined as involving the white matter of greater than 2 adjacent gyri, were also compared. Lesion resolution (defined as >50% decrease in the number of T2-bright areas) between the first and second MRI scans was evaluated as detailed elsewhere.7 No steps were taken to minimize the impact of differences in acquisition between the first and the second scans as this is not customarily used for clinic and trial scans.



Statistical analysis:

Calculations and statistical analyses were performed using Stata 10.0 statistical software (StataCorp, College Station, TX). Means (± standard deviations [SD]) or medians (with ranges) were used to summarize demographic, clinical and MRI data. Because the number of T2-bright foci is not normally distributed, results are presented as median with range, or proportion of patients with lesions in specific locations. Non-parametric tests were used to compare number of lesions between both groups (Mann-Whitney). Proportions were compared with chi square test. Multivariate logistic regression was performed, adjusted for race, to evaluate if children were more likely than adults to have the involvement of various regions on initial brain MRI. The effect of race/ethnicity on lesion number and location was evaluated in children. Patients with mixed race/ethnic ancestry (n=4) were dropped from these analyses.


Results

Patient characteristics at onset


We identified 41 POMS onset and 35 AOMS for whom initial brain scans were available. Patients’ characteristics are presented in Table 1. The main differences between groups included sex ratio, race, and proportion of patients with spinal cord and polyregional presentations.
Initial brain MRI scan

Time between symptom onset and first available brain MRI scan was longer in adults as their first available scan was in fact the baseline scan of the natural history study while in POMS, the first clinical scan was used. The MRI baseline differences for children and adults are summarized in Table 2. All but one POMS patients and all AOMS patients had at least one T2-bright area on the initial scan. The number of T2-bright foci at presentation was substantially higher in POMS than AOMS patients. In addition, children had a higher number and proportion of poorly defined T2-bright areas, large T2-bright areas, brainstem/cerebellar and corpus callosum involvement, and enhancing lesions. Deep grey matter involvement was similar in adults and children.

In the multivariate analysis, pediatric patients had more than four-fold increased odds of having infratentorial T2-bright foci compared to adults (OR=4.23, 95% CI [1.29, 13.83], p=0.017). There appeared to be no independent effect of race/ethnicity on infratentorial involvement (white, non-Hispanic vs others: OR=0.57, 95% CI [0.17, 1.93], p=0.36). Among POMS patients, no effect of race/ethnicity on the initial brain MRI was found in terms of total number of T2, large T2, and location of T2-bright foci (data not shown). White non-Hispanics tended to have less deep grey involvement (16.7% vs 41.7%, p=0.13), but more corpus callosum involvement (91.7% vs 54.2%, p=0.024) than others.
Follow-up brain MRI scan

All but one patient in each group had follow-up scans available. Data pertaining to the second brain MRI scans are presented in Table 4. The statistical analysis was repeated after removing the second scans obtained less than one month and more than one year after the first one. The results were not meaningfully changed after removing the second scans obtained less than one month and more than one year after the first one (data not shown). POMS patients had more new T2-bright foci and more Gd+ lesions on the repeat scan than adults. The proportion of patients on DMT at the time the follow-up scan was obtained was: 10% in POMS vs 36% in AOMS. Among POMS patients, there was no difference in terms of the number of new T2-bright foci and Gd+ lesions according to race/ethnicity (data not shown).


Comment

We report that POMS patients have a higher MRI disease burden at presentation and higher disease activity on follow-up scans than adults at the same disease stage seen at the same institution. This challenges the notion that POMS clinical onset may be closer to the biological disease onset3 and that POMS patients may experience a more benign clinical course than AOMS.1,12


POMS brain MRI scans at disease onset exhibit remarkable features compared to AOMS. First, our POMS patients have more frequent radiological infratentorial involvement than adults at the same disease stage. The more frequent radiological infratentorial involvement in children questions if the underlying biological processes at play are different in younger patients. It is unclear whether the timing of myelin maturation in POMS explains the selective infratentorial involvement. There appears to be a clear T2 relaxation time age dependency in brains from birth to early age (<5 years old),13 which could affect the sensitivity of detecting T2-weighted lesions in very young children compared to adults. However, this relaxation dependency is present in both the supra and infratentorial brain parenchyma,13 thus not likely to influence the proportion of infra/supratentotial lesions we observed in our study between AOMS and POMS subjects. Furthermore, whether the inflammatory response in POMS selectively targets antigens predominantly located in the posterior fossa remains to be determined. The selective infratentorial involvement on the initial brain MRI scan in POMS is consistent with our findings that POMS patients demonstrate more frequent clinical involvement of the brainstem or cerebellum at onset than adults.2 Second, pediatric patients with MS exhibit more ill-defined and large T2-bright foci on their initial scans than adults. This finding suggests that inflammatory processes in children may be less circumscribed than in adults, possibly as a result of more edematous reactions. We cannot exclude that differences at the level of the immature microglia and blood-brain barrier also contribute to these phenomena. Third, a significant resolution of the initial T2 lesion burden occurs in POMS patients, which was not demonstrated in AOMS. This is consistent with less destructive/more reversible lesions in children that could be explained by more edematous phenomenon, less axonal loss and demyelination, or better remyelination. The use of sophisticated imaging techniques such as multi-component T2 relaxometry, diffusion tensor imaging and spectroscopy may further characterize the main underlying processes.
Our findings have several implications. First, they suggest that at our institution, a large proportion of POMS patients may actually meet adult criteria for MS4,10 in terms of dissemination in space but also in terms of dissemination in time, consistent with a recent report.14 The higher disease activity in POMS compared to AOMS is also consistent with the observation in adults that younger patients have more frequent new Gd+ lesions on brain MRI scans than older patients.15 Second, the higher disease burden, frequency of infratentorial lesions and occurrence of new lesions at MS onset in children compared to adults are worrisome, as these features have been associated with more rapid accrual of disability in adults with MS.16-18 It remains to be confirmed by long-term follow-up whether our patients with POMS will have a worse prognosis in terms of disability progression, as we cannot rule out that better CNS plasticity in younger patients may in fact attenuate clinical progression in POMS patients with very active disease.
We report that nearly all POMS patients have abnormal brain MRI scans at disease onset. This is consistent with a previous publication.3 Although the total number of T2-bright foci at onset is not available from previous pediatric studies, the proportions of patients with various lesion locations reported for our POMS cohort match well previous.3,6,14 Similarly the proportion of pediatric patients with large lesions are within reported ranges.5,6 Finally, median numbers of T2-bright areas reported in several CIS studies in adults are in line with our AOMS findings.17,19,20 Of note, the median number of T2-bright foci on the initial scan of our POMS patients remains higher than values reported for AOMS patients in CIS studies.
Our study has several limitations. A referral bias may exist that could account for some of the reported group differences. Pediatric patients are seen at the Regional Pediatric MS Center at UCSF that serves the entire West Coast, while adults seen at UCSF tend to come from a smaller referral area, as several adult MS centers are available in California. This difference could bias the referral towards more severe pediatric patients being referred to our pediatric MS clinic. In addition, due to limited awareness that MS can affect children it is possible that children with milder cases may be undiagnosed for longer periods of time and therefore are not referred to us. Second, the MRI protocols used for children and adults were non-uniform. This difference, however, cannot explain the significant differences observed. The use of dedicated and conventional T2-weighted images in the adult MRI protocol and the predominant use of non-overlapping T2-FLAIR sequences (less sensitive in the posterior fossa) in children should have biased our findings towards detecting more posterior fossa lesions in adults, not the contrary. Third, that the MRI scans used for this analysis were obtained later in adults should also have biased towards higher T2 lesion burden in adults since most T2-bright foci tend to remain visible indefinitely in that age group.
The MRI differences between children and adult MS onset reported herein occur in the context of several demographic and clinical differences between groups (age, ethnic background, sex ratio, clinical onset location, monoregional vs polyregional onset). It is unclear if any of these demographic/clinical differences explains most of the reported MRI phenotype. Clearly, age was the main independent predictor for infratentorial involvement in the multivariate analysis, but also for other locations. Race/ethnicity maybe associated with some specific lesion location but this has to be confirmed in a larger cohort. The higher frequency of infratentorial involvement on MRI of POMS patients is striking, as clinical presentation involved brainstem/cerebellum equally in our two groups. These findings did not change substantially after removing polyregional presentations (data not shown).
The findings reported herein need to be replicated with a standardized MRI protocol in larger cohorts. In the future, the use of more sophisticated imaging techniques may help to further dissect biological differences related to age that pertain to qualitative and quantitative tissue injury and repair.
Acknowledgements: The UCSF regional Pediatric MS clinic belongs to the Pediatric MS network initiated by the NMSS. Dr Mowry has a NMSS Sylvia Lawry Fellowship Award and a Partners Clinical Fellowship Award. The adult natural history was supported by the NMSS (RG3240). Dr Waubant and Chabas are also supported by the Nancy Davis Foundation. Dr Pelletier is a Harry Weaver Neuroscholar of the National Multiple Sclerosis Society.
Table 1: Patients characteristics




Pediatric MS

(n=41)


Adult MS

(n=35)


P value

Mean age + SD

11.4 + 4.4

36.5 + 9.3




% white, non-Hispanic

40%

88.6%

<0.0001

% female

51.1%

77.1%

0.019

% polyregional onset

26.8%

0%

0.0009

Spinal cord (monoregional)

19.5%

57.1%

0.0007

Optic neuritis (monoregional)

21.9%

8.5%

0.110

Brainstem (monoregional)

36.6%

34.3%

0.834

Time in days between onset and 1st MRI available

Median (range)


13 (0, 129)



113 (48, 331)




<0.0001

Table 2: Characteristics of the first brain MRI scans.




Number of

Pediatric MS

(n=41)


Adult MS

(n=35)


P value

Total number of T2-bright foci

21

(0, 74)


6

(0, 76)


<0.0001

Non-ovoid, poorly defined T2-bright foci

3

(0, 55)


0

(0, 4)


0.0004

Ovoid, well-defined T2-bright foci


12

(0, 69)


5

(0, 75)


0.006

Large (>1 cm) T2-bright foci

4

(0, 26)


0

(0, 5)


<0.0001

Enhancing lesions


2

(0, 60)


0

(0, 5)


<0.0001

Juxtacortical lesions

9

(0, 48)


1

(0, 8)


<0.0001

Periventricular lesions

6

(0, 21)


2

(0, 12)


0.0005

Cerebellar lesions

0

(0, 8)


0

(0, 2)


0.012

Brainstem lesions

1

(0, 6)


0

(0, 3)


0.002

Corpus callosum lesions

1

(0, 8)


0

(0, 3)


0.073

Table 3: Proportion of patients with specific lesion types and locations.







Pediatric MS

(n=41)


Adult MS

(n=35)


P value

Large T2-bright foci (>1 cm)

87.8%

48.6%

0.0002

Enhancing lesions

68.4%

21.2%

0.0001

Confluent T2-bright foci

19.5%

22.8%

0.72

Infratentorial T2-bright foci

68.3%

31.4%

0.001

- Cerebellum T2-bright foci

41.5%

17.1%

0.021

- Brainstem T2-bright foci

58.5%

25.7%

0.004

Corpus callosum T2-bright foci

63.4%

40%

0.04

Juxta-cortical T2-bright foci

90.2%

57.1%

0.0009

Deep grey matter T2-bright foci

34.1%

28.6%

0.602

Table 4: MRI characteristics on the second brain scans.






Pediatric patients

(n=40)


Adult patients

(n=34)


P value

Time between 1st and 2nd MRI*

106 days

(10,1512)



196 days

(92, 658)



0.007

New T2-bright foci*

2.5

(0, 48)


0

(0, 32)


<0.0001

Gadolinium-enhancing foci*
Mean + Standard deviation

0

(0, 13)


2.2 + 3.7

0

(0, 4)


0.15 + 0.7

0.0001

Reduction of T2-bright signal >50% on follow-up scan

22.5%

0

0.0032

*median, range

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LEGENDS
Table 1: Patients’ characteristics are provided for children and adult MS patients.
Table 2: MRI characteristics on the first brain scans.

Numbers of lesions are presented as median and range for various lesion types and locations. The Mann Whitney test was used to compare groups as the distribution of lesions was not normal.


Table 3: Proportion of patients with specific lesion types and locations.

The chi square test was used to compare the proportions in both groups.


Table 4: MRI characteristics on the second brain scans.

This table presents the changes between the first and 2nd available brain MRI scans for children and adult patients. Numbers of lesions are presented as median and range for various lesion types and locations (unless mean or percentage of patients is specified). The Mann Whitney test and the chi square test were used to compare groups as appropriate.


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