Spinal muscular atrophy (SMA) is an inherited neuromuscular (muscle nerve) disorder that causes muscle weakness and breakdown over time. There are five main types of SMA — types 0, 1, 2, 3, and 4. Type 0 is the most severe form of SMA and begins before birth, while type 4 is the mildest and begins in adulthood.

The Hammersmith Functional Motor Scale (HFMS) was developed for individuals with SMA type 2 and SMA type 3 to evaluate their physical abilities. The scale may be used for both children and adults.

What Is the Hammersmith Functional Motor Scale for SMA?

The HFMS was created for people with SMA whose mobility is limited. This tool was originally developed to be used for children with SMA types 2 and 3 who are more than 30 months of age. The purpose of the scale is to gather information on a person’s disease progression and their motor (movement) abilities. The scale consists of 20 scored activities, with a maximum score of 40 points. It’s designed to be easy to use, quick, self-explanatory, reliable, and reproducible.

Scores from the Hammersmith Functional Motor Scale help provide a history of an individual’s physical abilities. Your HFMS record can be used to confirm changes in your motor ability.

Why Is the Hammersmith Functional Motor Scale Important?

The HFMS is an important tool for individuals with SMA and their healthcare providers. It’s also used by researchers in clinical trials who are testing new treatments and supportive technologies for people with SMA. The scores gathered from the scale help provide a personal history of an individual’s physical abilities. Because of this, a person’s HFMS record can be used to confirm changes in their motor ability.

Tracking Disease Progression and Evaluating Treatment

The HFMS is an important tool to track changes in motor function skills over time. Doctors need functional scales like the HFMS to determine whether a person’s motor functions are getting better or worse. This will help assess whether their current treatments are effective or whether changes should be made to their treatment plan.

Validating Treatment

Three treatments have been approved by the U.S. Food and Drug Administration (FDA) for people with SMA. Two are disease-modifying therapies — nusinersen (Spinraza) and risdiplam (Evrysdi) — and the third is a gene therapy called onasemnogene abeparvovec-xioi (Zolgensma). More research is needed to learn more about SMA and to determine the impact of these treatments. Assessments like the HFMS can help researchers monitor the success of these new therapies in treating those with SMA, as well as the efficacy of experimental treatments currently in clinical trials. Keep in mind that the HFMS is just one tool that providers can use to assess the overall health of people with SMA. Providers consider more than just the HFMS score when making treatment recommendations.

Assessments like the HFMS help researchers monitor the effectiveness of SMA therapies and evaluate experimental treatments currently in clinical trials.

What Does the Hammersmith Functional Motor Scale Assessment Involve?

The HFMS consists of 20 items. Originally, pediatric SMA professionals developed the scale to evaluate the physical abilities of children with SMA. The scale’s creators chose these 20 items based on their ability to measure the physical functioning of children with both SMA types 2 and 3. Now, an expanded version of the HFMS is used for people of all ages who have type 2 or 3 SMA.

This clinical tool should be administered by professionals who have specialized experience working with children with SMA, such as trained clinicians, physical therapists (physiotherapists), occupational therapists, and researchers. People who aren’t trained in this tool might conduct the test or score children incorrectly.

This specialist asks the person being evaluated to perform activities, both supported and not supported. Some of these activities include:

• Chair sitting
• Standing
• Walking
• Rolling over
• Moving from lying to sitting

The administrator then grades the completion and quality of the person’s movement. If the person is unable to complete the activity, a score of 0 is recorded. If they can perform the movement with some assistance, the score is a 1. If they can complete the action unaided, a 2 is recorded. These activity scores are then added together. Forty is the highest total score that can be achieved on the original HFMS.

Does the Hammersmith Functional Motor Scale Diagnose SMA?

The HFMS does not diagnose spinal muscular atrophy. SMA is often diagnosed through a series of blood tests. The diagnostic process may also include electromyography, nerve conduction velocity studies, muscle biopsies, and other tests.

The Revised Hammersmith Scale is often used because it’s seen as being more accurate than older tests at measuring changes in people who received early treatment.

Newer Versions of the Hammersmith Scale

Since the original HFMS was designed in 2003, there have been additions to the scale. Additionally, other versions of the assessment have been developed.

Modified Hammersmith Functional Motor Scale

Fatigue may impact a person’s ability to complete certain tasks over time. The Modified Hammersmith Functional Motor Scale includes the same items and scoring as the original HFMS, but it has a different order of tests to minimize the potential fatigue of the person undergoing the assessment. The different order is intended to minimize the impacts of fatigue on the person’s results.

Hammersmith Functional Motor Scale Expanded

The Hammersmith Functional Motor Scale Expanded (HFMSE) is a longer version of the original HFMS. It contains the same original items, plus 13 additional items designed for people with SMA type 3 who are ambulatory. These new items (including squatting and jumping) were added to the HFMSE after consulting the Gross Motor Function Measure — an assessment originally made for people with cerebral palsy. This expanded assessment tool contains 33 items and has the same measurement scale as the original. Its total possible score is 66.

Revised Hammersmith Scale

In 2014, the HFMS and other SMA functional scales came under criticism for their accuracy, scoring, and reliability. An expert group of SMA professionals met and reviewed the scales with the goal of improving the original assessment. The Revised Hammersmith Scale (RHS), which contains 36 items with a maximum score of 69, was created. It includes two timed tests to evaluate strength and includes references to motor milestones from the World Health Organization (WHO).

The Revised Hammersmith Scale is generally the preferred assessment because it’s seen as being more accurate than older tests at measuring changes in people who have received early treatment. Ultimately, the test that is used depends on the spinal muscular atrophy type, the age of the person being assessed, and the severity of their symptoms.

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