New Screening Tool Shows Success in Identifying Movement Disorders in Patients with Inborn Errors of Metabolism

Marina A.J. Tijssen, MD, PhD

Published in Movement Disorders, investigators developed an easy-to-use clinical screening tool to detect moderate and severe movement disorders in patients aged more than or 4 years of age with inborn error of metabolism (IEM).¹ Researchers proposed that the tool can contribute to the referral patients to movement disorder specialists for further evaluation and possibly treatment.

All told, the specialists scored a movement disorder in 130 of the 165 ratings (78.8%), concering 44 patients (80%) in whom the majority of the specialists concluded that a movement disorder was present. Above all, there was moderate inter-rater agreement (κ = .420, P <.001) on the presence of a movement disorder. Notably, in consideration for a movement disorder diagnosis, only moderate and severe movement disorders, the inter-rater agreement increased significantly (κ = .900, P <.001).

Senior author Marina A.J. Tijssen, MD, PhD, professor of neurology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands, and colleagues wrote, “In this study, we show that movement disorder specialists highly agree on the presence of moderate and severe movement disorders in patients with IEMs. The recognition of moderate and severe movement disorders is particularly important because treatment was also mainly suggested for these groups.”¹

Patients with different IEMs consented to share videos with experienced international movement disorder specialists (n = 12), including 3 neurologists trained in pediatric neurology. Movement disorder specialists scored videos blindly and independently based on presence and severity on dominant movement disorder and other associated movement disorders. Additionally, specialists scored videos according to the five most informative parts of examination (from 1 [most important] to 5), and suggested treatment of the movement disorder.

Presence and subtype of the movement disorder were determined in the inter-rater agreements and items were chosen to be incorporated into the screening tool according to ranking as well as consensus. Movement disorder specialists scored 55 patients with a mean age of 30.2 years of age with 15 different IEMs, comprising of 2 children between 4 and 12 years of age, 16 adolescents between 12 and 18 years of age, and 37 adults older than 18 years of age.

The specialists failed to score a movement disorder in 11 patients (20%). A 100% observed agreement between all 3 raters was reached for 39 of the 55 patients (70.9%), of which 35 (63.6%) were considered with a movement disorder. In 9 patients (16.4%), 2 raters scored a movement disorder and 1 did not.

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In terms of the consensus dominant phenotype, dystonia was the most frequently scored (27.3%), followed by ataxia (10.9%), chorea (5.5%), myoclonus (3.6%), parkinsonism (3.6%), and tremor (1.8%). Variety could be explained partially as patients with an IEM often present complex movement disorder phenotypes.^2,3 Treatments were suggested mainly to patients with moderate (34.3%) or severe (6.8%) movement disorders in comparison to mild (57%).

The inter-rater agreement on the dominant movement disorder phenotype, including the class “no movement disorder,” was fair (κ = .241, P <.001). Best overall inter-rater agreement was reached for ataxia (κ = .518, P <.001) and worst for the rest group “other,” mainly indicating spasticity (κ = .185, P = .017).

In design of the screening tool, investigators noted, “Observation of the arms (eg, including arms in rest, arms stretched forward in several positions, and finger-to-nose test); walking, writing, and drawing a spiral; examination of eye movements; and tapping were considered as most important.”¹

Limitations included lack of gold standard for the diagnosis of movement disorders. Electrophysiological testing was not available for most patients in the study to help confirm tremor and myoclonus. Videos examined patients which might have influenced the outcome as some symptoms were not visible on video. In addition, videos were not standardized completely, examination segments were variable. Children were underrepresented in the sample, although movement disorders in children might be detected using the screening tool.

"In the near future, we will validate and further design the screening tool to see whether it can be used to select patients who need to be referred to a multidisciplinary team for further evaluation and, if necessary, treatment of the movement disorder,” Tijssen et al noted.¹

REFERENCES
1. Koens LH, Klamer MR, Sival DA, et al. A Screening Tool to Quickly Identify Movement Disorders in Patients with Inborn Errors of Metabolism. Mov Disord. 2023;10.1002/mds.29332. doi:10.1002/mds.29332
2. Koens LH, Kuiper A, Coenen MA, et al. Ataxia, dystonia and myoclonus in adult patients with Niemann-Pick type C. Orphanet J Rare Dis. 2016;11(1):121. Published 2016 Sep 1. doi:10.1186/s13023-016-0502-3
3. Ferreira CR, Martinelli D, Blau N. Clinical and biochemical footprints of inherited metabolic diseases. VI. Metabolic dermatoses. Mol Genet Metab. 2021;134(1-2):87-95. doi:10.1016/j.ymgme.2021.07.005