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Modified Hammersmith Functional Motor Scale for Children with Spinal Muscular Atrophy (MHFMS-SMA
Availability
Please visit this website for more information about the instrument: Modified Hammersmith Functional Motor Scale for Children with Spinal Muscular Atrophy
 
For questions related to content and test use, please contact Kristin Krosschell, PT, MA, PCS: k-krosschell@northwestern.edu
Classification
Supplemental - Highly Recommended: : *Mitochondrial Disease (Mito), **Spinal Muscular Atrophy (SMA)
 
*Recommendations for use: Indicated as a primary outcome measure in treatment trials of young non-ambulatory children with Spinal Muscular Atrophy (SMA).
 
**Recommendations for use: Indicated for individuals with type 2 (intermediate SMA) and type 3 (juvenile SMA) to evaluate their physical abilities.
Short Description of Instrument
The Modified Hammersmith Functional Motor Scale for Children with Spinal Muscular Atrophy (MHFMS-SMA) (Krosschell, et al. 2006) is an adaptation of the original Hammersmith Functional Motor Scale for Children with SMA (Main et al., 2003). The original Hammersmith Functional Motor Scale for Children with SMA was modified to establish a standard measure of functional ability in children with non-ambulant spinal muscular atrophy Types II and III for use in longitudinal multi-center clinical trials. Concrete operational definitions were developed and scoring criteria were clarified to minimize potential ambiguities in the administration and scoring of the test. In addition, after a pilot study, item order of 20 motor tasks was modified to minimize position changes and to decrease fatigue and undue stress on the children during testing (Krosschell et al., 2006). The MHFMS is currently in use to assess gross motor abilities of non-ambulant children with SMA in multiple research trials as well as in clinical settings.
 
The MHFMS-Extend was later developed to address ceiling effects in stronger ambulant children with SMA. The MHFMS-Extend consists of the MHFMS and an extended gross motor module and was developed to allow for assessment of stronger children with SMA Type II and for assessment of ambulant children with SMA Type III. Items selected for the MHFMS-Extend were chosen based on functional, clinical and research applicability after careful assessment of a large group of children with SMA Type III and a group of stronger Type II children. Additional test modules include a Timed Test Module and a Fine Motor Module. The test manuals for each were developed to assure standardized assessment in clinical trials and to allow for training of new trial evaluators and clinicians working with children with SMA.
 
Time to Administer:
15-30 minutes.
 
Administration: Should be administered by expert clinicians.
Comments/Special Instructions
A Revised Hammersmith Scale (RHS) for SMA was developed by Ramsey et al. (2017) and consists of 36 items and two timed tests. (Ramsey et al., 2017) The RHS is used to capture improvement in patients with type 2 and 3 SMA and evolving phenotypes. (Ramsey et al., 2022)
Scoring and Psychometric Properties
Scoring: The Hammersmith Scale is scored on a 3-point ordinal scale. Each item is scored as 0 (unable), 1 (partially completes), or 2 (completes independently). A total score is calculated ranging from 0-40, with 40 being the highest score. A sub-score is not calculated.
Psychometric Properties: Krosschell et al (2006) assessed the intra- and interrater reliability and the test-retest stability of a modified version of the scale. Both intra- and interrater reliability were established. Intra-rater reliability between the first and second test had a reliability coefficient of 0.99 indicating excellent reliability within a given rater. Interrater reliability score and rescore reliability assessed by intraclass correlation coefficient demonstrated an interrater reliability of 0.953 at a 95 % confidence interval (0.913, 0.982). Results indicated that the scale is reliable and stable over a 6-month period. Reliability was maintained when patient sample criteria were expanded to include children younger than 30 months and children with popliteal angles greater than 20 degrees.
 
These data established the modified Hammersmith functional motor scale for children with spinal muscular atrophy as a reliable instrument for use in multi- center treatment trials in non-ambulant spinal muscular atrophy children. Data from this study provided additional support for the use of original scale items in terms of ease of administration, usefulness and reliability, while incorporating modifications to optimize its use in a multi-center clinical research setting. The outcome measures were sensitive to small changes in functional ability. The modified Hammersmith functional motor scale appeared to be well suited for use as a primary outcome measure in treatment trials of young non-ambulatory children with SMA who are able to sit unsupported. Although it theoretically could be used in weaker type 2 children who have lost the ability to sit or in stronger SMA children who have the ability to stand or even take a limited number of steps unsupported, these populations are less ideal for use of the scale as it currently stands. Scores assessed in children as young as 24 months of age, and in those with hamstring contractures manifesting a popliteal angle greater than 20 degrees appear to be as reliable as in older children and children without contractures.
 
Items selected for the MHFMS-Extend were chosen based on functional, clinical and research applicability after careful assessment of a large group of children with SMA Type III and a group of stronger Type II children. Additional test modules include a Timed Test Module and a Fine Motor Module which could be considered as add-on modules. The test manuals for each were developed to assure standardized assessment in clinical trials and to allow for training of new trial evaluators and clinicians working with children with SMA.
 
Validated in SMA pediatric patients. Children (2 to 11 Years); Adolescents (12 to 15 Years)
Rationale/Justification
Strengths: The Hammersmith functional motor scale for children with SMA is intended to be sensitive to those functional motor deficits of children with SMA that result directly from weakness. Hammersmith functional motor scale for children with SMA has been shown to be both quick to administer and reliable in non-ambulant children with SMA as young as 30 months of age (Main et al, 2003), when other tools such as myometry or the medical research council (MRC) scale cannot be easily or reliably performed.
 
The Hammersmith functional motor scale for children with spinal muscular atrophy was modified to establish a standard measure of functional ability in children with non-ambulant spinal muscular atrophy types 2 and 3 in a longitudinal multi-center clinical trial. In children under 5 years of age, functional motor scales may be more appropriate than myometry in the assessment of strength in children with SMA, as motivation for maximum performance need not depend upon comprehension of the purpose of the task. Scales targeted to assess functional ability with disease-specific and strength-specific tasks may have the potential to exceed direct measures of power in sensitivity and reliability (Main et al, 2003, Chung et al, 2004, Iannaccone, 2002).
 
This tool has potential applications for young children with mitochondrial myopathies and marked weakness, particularly those with mtDNA depletion myopathy secondary to thymidine kinase 2 (TK2) deficiency which has an SMA phenotype and may present in infancy.
 
Weaknesses: Functional testing may not be able to detect subtle changes and/or monitor for changes in muscle strength (Moxley 1990). However, functional tests are better at assessing outcomes (activities of daily living) that may be more meaningful to patients (Krosschell et al 2006).
References
Key Reference:
Moxley RT 3rd. Functional testing. Muscle Nerve. 1990;13 Suppl:S26-9.
 
Additional References:
Chung BH, Wong VC, Ip P. Spinal muscular atrophy: survival pattern and functional status. Pediatrics. 2004 Nov;114(5):e548-53.
 
Iannaccone ST; American Spinal Muscular Atrophy Randomized Trials (AmSMART) Group. Outcome measures for pediatric spinal muscular atrophy. Arch Neurol. 2002 Sep;59(9):1445-50.
 
Krosschell KJ, Maczulski JA, Crawford TO, Scott C, Swoboda KJ. A modified Hammersmith functional motor scale for use in multi-center research on spinal muscular atrophy. Neuromuscul Disord. 2006 Jul;16(7):417-26.
 
Main M, Kairon H, Mercuri E, Muntoni F. The Hammersmith functional motor scale for children with spinal muscular atrophy: a scale to test ability and monitor progress in children with limited ambulation. Eur J Paediatr Neurol. 2003;7(4):155-9.
 
Ramsey D, Ramdharry G, Scoto M, Muntoni F, Wallace A; SMA REACH UK network. Revised Hammersmith Scale for spinal muscular atrophy: Inter and intra-rater reliability and agreement. PLoS One. 2022 Dec 21;17(12):e0278996.
 
Ramsey D, Scoto M, Mayhew A, Main M, Mazzone ES, Montes J, de Sanctis R, Dunaway Young S, Salazar R, Glanzman AM, Pasternak A, Quigley J, Mirek E, Duong T, Gee R, Civitello M, Tennekoon G, Pane M, Pera MC, Bushby K, Day J, Darras BT, De Vivo D, Finkel R, Mercuri E, Muntoni F. Revised Hammersmith Scale for spinal muscular atrophy: A SMA specific clinical outcome assessment tool. PLoS One. 2017 Feb 21;12(2):e0172346.
 
Document last updated October 2024