The Symbol Digit Modalities Test is an effective cognitive screen in pediatric onset multiple sclerosis (MS)

https://doi.org/10.1016/j.jns.2014.04.006Get rights and content

Highlights

  • The SDMT is evaluated as a screen for cognitive impairment in pediatric MS.

  • Pediatric MS participants are compared to other neurological disorders and controls.

  • The SDMT is compared to the composite neuropsychological performance.

  • Clinical features that predict SDMT performance in pediatric MS are identified.

Abstract

Objective

To evaluate the Symbol Digit Modalities Test (SDMT) as a tool for identifying pediatric-onset MS patients at risk for cognitive impairment.

Background

The SDMT is a brief measure of cognitive processing speed that is often used in adult MS patients. Approximately one-third of pediatric-onset MS patients have cognitive impairment and there is a need for an effective screening instrument.

Design/methods

Seventy (70) consecutive outpatients with pediatric-onset MS underwent clinical evaluations including the SDMT and were compared to those with other pediatric neurological diagnoses (OND, n = 40) and healthy controls (HC, n = 32). A subset of the MS group and all healthy controls completed neuropsychological evaluation within one year of SDMT administration.

Results

The MS group performed worse on the SDMT compared to the HC group (p = 0.02). Thirty-seven percent (37%) of the MS, 20% of the OND, and 9% of HC groups scored in the impaired range. For MS participants who underwent neuropsychological testing (n = 31), the SDMT showed 77% sensitivity and 81% specificity for detecting neuropsychological impairment when administered within one year and reached 100% sensitivity when the interval was under two months (n = 17). Overall, older age and increased disability predicted poorer SDMT performance (age r =  0.26, p = 0.03) and the Expanded Disability Status Scale score or EDSS (r =  0.47, p < 0.001), while a history of optic neuritis predicted better performance (p = 0.04). Optical coherence tomography measures were not related to SDMT performance.

Conclusion

In this preliminary study, the SDMT was an effective brief screen for detecting cognitive impairment in pediatric-onset MS.

Introduction

The Symbol Digit Modalities Test (SDMT) is a brief test of information processing speed that has become the most commonly used cognitive measure in adults with multiple sclerosis (MS) [1], [2], [3]. Approximately one-half of the adult MS population is estimated to have some degree of cognitive impairment [4] and the SDMT has been demonstrated to be a sensitive and reliable indicator of those at risk [4], [5], [6].

In a sample of 100 adults with MS compared to 50 demographically-matched healthy controls, Parmenter and colleagues [7] found that the SDMT was an effective brief screen correctly categorizing 72% of those with cognitive impairment on a more extensive battery of test (the Minimal Assessment of Cognitive Function in MS or MACFIMS). The SDMT is one of the three measures recommended by for the Brief International Cognitive Assessment for MS (BICAMS) [4]. Performance on the SDMT is a strong predictor of employment status in MS patients, and those who are unemployed perform worse on SDMT testing [8].

The SDMT has been linked to MS-related brain MRI pathology [2], [9], [10] including brain MRI total lesion load [11], cortical lesion number, cortical lesion volume, and overall white matter lesion volume [12]. In one MS sample, the SDMT score was also positively correlated with concentration of CSF amyloid-beta, with reductions shown to be a marker of cognitive impairment [13]. Worsening SDMT has been used to detect change within an individual MS patient. For instance, MS patients experiencing an acute relapse worsened on the SDMT when compared to in MS patients who were neurologically stable [14].

While typically affecting adults, up to 5% of MS cases are reported in children and adolescents. One-third of pediatric-onset MS patients have some degree of cognitive impairment on neuropsychological testing [15], [3]. Cognitive deficits in pediatric-onset MS patients overlap with those found in adults [3] and commonly include information processing speed, working memory, verbal learning, and visuospatial abilities. However, as in adults, deficits may be mild and therefore difficult to identify during routine monitoring visits.

It is especially critical to detect cognitive involvement in pediatric-onset MS patients because of both the long-term effects of early cognitive impairment and the potential mitigating effects of early intervention. Children and adolescents with MS may be at even greater risk for cognitive impairment over time as a consequence of ongoing demyelination, which prevents normal maturation of neural connections [16]. A brief and sensitive screen for cognitive impairment is needed for pediatric-onset MS patients [4].

Despite the wide use of the SDMT in adult MS, few studies have reported SDMT performance in pediatric-onset MS. In an Italian sample, 63 pediatric MS participants, aged 8 to 18 years, were found to score lower than 57 healthy controls on the SDMT, but the mean difference did not reach statistical significance [16]. In a U.S. sample, 43 pediatric MS participants, ages 6 to 17 years, scored significantly lower than 45 healthy controls on the SDMT [8]. A Canadian study of 35 pediatric MS patients compared to 33 controls found that a greater proportion of MS patients had SDMT scores falling below 1.5 SD from the mean (12% vs. 0%) [17]. Little is known concerning the relationship between SDMT performance and other clinical characteristics of pediatric-onset MS, and whether it is an effective screening tool to identify those at risk for cognitive impairment.

To better understand the utility of the SDMT for the pediatric-onset MS patient population, we evaluated the SDMT as a screen for cognitive impairment in pediatric-onset MS patients compared to pediatric neurologic outpatients seen at our outpatient center diagnosed with a neurologic diagnosis other than MS (other neurological diagnosis or OND) and to healthy pediatric controls (HCs). SDMT performance was examined in relation to MS clinical descriptors and, for a subset of patients, performance on a battery of neuropsychological tests.

Section snippets

Method

This study was approved by the Stony Brook Institutional Review Board. In the case of minors, a parent provided consent, and participants signed assent forms.

MS and OND participant SDMTs were collected from consecutive patients presenting for neurological evaluation at the Lourie Center for Pediatric MS between May 2009 and October 2013. MS participants met criteria for pediatric-onset MS (disease onset prior to age 18 years) [18]. OND participants were pediatric patients who came to the Lourie

Demographics

Participants were seventy (70) pediatric-onset MS patients, forty (40) OND patients, and thirty-two (32) HCs. The OND group had a range of diagnoses including: migraine (20%), non-specific sensory symptoms with normal brain magnetic resonance imaging results (17.5%), optic neuritis (12.5%), NMO (12.5%), ADEM (7.5%), leukodystrophy (5%), transverse myelitis (5%), autoimmune lymphoproliferative disease (2.5%), developmental delay (2.5%), Lyme disease (2.5%), meningoencephalitis (2.5%), neuropathy

Discussion

We found that the SDMT is an effective screen for cognitive impairment in pediatric-onset MS. The MS participants had worse performance than both pediatric patients with other neurological diagnoses and pediatric healthy controls. Overall, 37% of the MS participants were impaired on the SDMT. This can be compared to an impairment rate of 32% in the subset of MS participants who received neuropsychological evaluation. It is notable that an impairment rate of approximately one-third of pediatric

Conclusion

In summary, as in adults with MS, these preliminary data support the use of the SDMT as a screen for cognitive function in pediatric-onset MS. Patients found to have a SDMT in the impaired range or those with a marked decline on a repeated visit would be the best candidates for neuropsychological evaluation to confirm and classify degree of cognitive impairment.

Conflict of interest

The authors declare that there is no conflict of interest.

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