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SCALES OF

SMA

Measuring the progression of SMA. Following an initial increase and peak in motor skills from baseline, the subsequent downturn marks the onset of SMA, with disease progression (and loss of motor skills) being most rapid in the early stage compared to the later stage.1

The characters shown are real patients and the required consent to use their stories has been obtained from the patients and families. Photographs are for illustrative purposes only.

SCALES TO HELP QUANTIFY SMA

Several motor function scales have been developed that are useful in quantifying the natural history of spinal muscular atrophy (SMA), as well as the response to investigational therapeutic agents in clinical trials.2-4

Quantifying the natural history of SMA

A graphical approximation, divided by group subtypes, of what natural history studies tell us about the evolution of patients with SMA

MEASURING THE PROGRESSION OF SMA

The natural progression of SMA involves loss of motor function. Following an initial increase, a peak in motor skills and subsequent downturn marks the onset of SMA, with disease progression (and loss of motor skills) being most rapid in the early stage.1

An illustration of the range of function across the spectrum of SMA1,2

Adapted from Swoboda KJ et al, 2007 1

The Children’s Hospital of Philadelphia InfantTest of Neuromuscular Disorders (CHOP INTEND)

This test is used to evaluate the motor skills of infants with SMA:2,5

  • Includes 16 items used to assess motor skills and usually used for patients with very limited motor skills (e.g. not able to sit, poor head control)

  • Each item is graded on a scale of 0-4, where 0 represents no response to a particular test, and 4 represents a complete response

  • Total score ranges from 0 to 64 and declines by ~1.3 points per year on average6

This test is also used to assess SMA Type I patients:2

  • For those with very limited motor skills (e.g. not able to sit, poor head control)

  • Total score ranges from 0 to 64 and declines by ~1.3 points per year on average6

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CHOP INTEND:
1 Spontaneous movement (upper extremity) 9 Shoulder flexion & elbow flexion
2 Spontaneous movement (lower extremity) 10 Knee extension
3 Hand grip 11 Hip flexion and foot dorsiflexion
4 Head in midline with visual stimulation 12 Head control
5 Hip adductors 13 Elbow flexion
6 Rolling: elicited from legs 14 Neck flexion
7 Rolling: elicited from arms 15 Head / neck extension
8 Shoulder and elbow flexion and horizontal abduction 16 Spinal incurvation

Hammersmith Infant Neurological Examination (HINE)

  • HINE is a simple motor function assessment tool designed to evaluate motor skills in infants from 2 months to 2 years of age:7

  • Exam includes 26 items that provide a comprehensive assessment of an infant’s neuromuscular development7

  • Each item is scored from 0 to 3, with a total possible score of 787

The motor milestones portion of the HINE includes 8 items8

Voluntary grasp
No grasp Uses whole hand
Index finder and thumb but immature grasp Pincer grasp
Ability to kick (in supine)
No kicking Kick horizontal, legs do not drift Upward (vertical)
Touches leg Touches toes
Head control
Unable to maintain upright Wobbles All the time upright
Rolling
No rolling Rolling to side
Prone to supine Supine to prone
Sitting
Cannot sit Sit with support at hips Props
Stable sit Pivots (rotates)
Crawling
Does not lift head On elbow On outstretched hand
Crawling flat on abdomen On hands and feet
Standing
Does not support weight Supports weight
Stands with support Stands unaided
Walking
No walking Bouncing
Cruising (holding on) Walking independently
1 1 1 1 1 1

Mercuri et al, Neuromuscular Disorder, 2018

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Finkel et al, Neuromuscular Disorder, 2018

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Hammersmith Functional Motor Scale—Expanded (HFMSE)

HFMSE is a validated measure that has been used in several clinical trials to evaluate the motor function of children with spinal muscular atrophy.

This exam adds 13 clinically relevant items from the Gross Motor Function Measure (GMFM) related to lying / rolling, crawling, crawling / kneeling, standing, and walking / running / jumping:4,9

  • Exam has 33 items that are scored on a scale of 0 to 2

  • Total score ranges from 0 to 66, with lower scores indicating poorer motor function

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SITTING ROLLING TRANSITIONING⁠/​CRAWLING
ITEMS 1-4 ITEMS 5-9 ITEMS 10-17
STANDING⁠/​STEPPING TRANSITIONING⁠/​KNEELING SQUAT⁠/​JUMP
ITEMS 18-20 ITEMS 21-27 ITEMS 28-29
STAIRS
ITEMS 30-33

Electrophysiologic measurements

  • In SMA, electrophysiologic measurements may be used to assess the health of motor neurons10

  • Compound muscle action potential (CMAP) response is a measure of the electrophysiologic output from a specific muscle or muscle group following stimulation of a peripheral nerve11

  • Motor unit number estimation (MUNE) is a method that estimates the number of motor units supplying a specific muscle12

    • MUNE values are calculated from the ratio of the maximal CMAP to the average single motor neuron potential (SMUP)12

    • SMUP is measured by moving a stimulating electrode along a motor nerve at multiple points12

CMAP may decrease rapidly in some individuals withspinal muscular atrophy10

  • Trendlines represent declines in CMAP in individuals with spinal muscular atrophy

  • The shaded areas indicate estimated minimum values in people without SMA‌10

Adapted from Swoboda et al 10

Reductions in CMAP are associated with the onset of symptoms in individuals with infantile-onset (Type I) SMA

Adapted from Swoboda et al 10

Early diagnosis may be an important consideration in the treatment of spinal muscular atrophy. The pattern of motor neuron loss seen in SMA suggests that a treatment for infantile-onset (Type I) SMA should be administered as early as possible, including the presymptomatic period before significant loss of motor neurons.13

Find out more about the different types of SMA.

Types of SMA
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The characters shown are real patients and the required consent to use their stories has been obtained from the patients and families. Photographs are for illustrative purposes only.

References

1. Swoboda KJ, et al. Perspectives on clinical Trials in Spinal Muscular Atrophy. J Child Neurol 2007;22(8):957-966.

2. Glanzman AM, et al. The Children’s Hospital of Philadelphia Infant Test of Neuromuscular Disorders (CHOP INTEND): test development and reliability. Neuromuscul Disord 2010;20(3):155-161.

3. De Sanctis R., et al. Developmental milestones in type I spinal muscular atrophy, Neuromuscular Disorders. Volume 26, Issue 11, 2016, 754-759.

4. Mercuri E, et al. Patterns of disease progression in type 2 and 3 SMA: implications for clinical trials. Neuromuscul Disord 2016;26(2):126-131.

5. Spinal Muscular Atrophy Clinical Research Center. CHOP INTEND for SMA Type I score sheet. [online] Mar 2013 [cited 2020 Sep 30]. Available from: URL: http://columbiasma.org/docs/cme-2010/CHOP%20INTEND%20for%20SMA%20Type%20I%20-%20Score%20Sheet.pdf.

6. Finkel RS, et al. Observational study of spinal muscular atrophy type I and implications for clinical trials. Neurology 2014;83:810-817.

7. Romeo DM, Ricci D, Brogna C, Mercuri E. Use of the Hammersmith Infant Neurological Examination in infants with cerebral palsy: a critical review of the literature. Dev Med Child Neurol 2016;58(3):240-245.

8. British Paediatric Neurology Association. Hammersmith Infant Neurological Examination. [online] Juli 2017 [cited 2021 Jan 29]. Available from: URL: https://bpna.org.uk/userfiles/HINE%20proforma_07_07_17.pdf.

9. The Pediatric Neuromuscular Clinical Research Network for SMA. Expanded Hammersmith Functional Motor Scale for SMA (HFMSE). [online] Mar 2009 [cited 2016 Apr 25]. Available from: URL: http://columbiasma.org/docs/cme-2010/Hammersmith%20Functional%20Motor%20Scale%20Expanded%20for%20SMA%20Type%20II%20and%20III%20-%20Manual%20of%20Procedures.pdf.

10. Swoboda KJ, et al. Natural history of denervation in SMA: relation to age, SMN2 copy number, and function. Ann Neurol 2005;57(5):704-712.

11. Arnold WD, et al. Electrophysiological motor unit number estimation (MUNE) measuring compound muscle action potential (CMAP) in mouse hindlimb muscles. J Vis Exp 2015;103:1-8.

12. Bromberg MB, Swoboda KJ. Motor unit number estimation in infants and children with spinal muscular atrophy. Muscle Nerve 2002;25(3):445-447.

13. Finkel RS. Electrophysiological and motor function scale association in a pre-symptomatic infant with spinal muscular atrophy type I. Neuromuscul Disord. 2013;23(2):112-115.