Spinal muscular atrophy (SMA) is an inherited neuromuscular disorder that causes muscle weakness and degeneration over time. The Hammersmith Functional Motor Scale (HFMS) was developed for individuals with SMA type 2 (intermediate SMA) and SMA type 3 (juvenile SMA) to evaluate their physical abilities. The scale may be used for both children and adults.
There are five main types of SMA that account for 95 percent of cases: 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 HFMS is used for people with SMA types 2 and 3 — especially for those whose mobility is limited.
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 — including sitting, rolling, crawling, and standing — that are designed to be easy to use, quick, self-explanatory, reliable, and reproducible.
The HFMS is an important tool for individuals and health care providers. It’s even 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. A person’s HFMS record can be used to confirm changes in their motor functions.
The HFMS is an important tool to track changes in a person with SMA’s motor-function skills over time. Doctors need functional scales like the HFMS to determine whether a person’s motor functions are improving. This will help assess whether their current treatments are effective or whether changes should be made to their treatment plan.
Three treatments (disease-modifying therapies) have been approved by the U.S. Food and Drug Administration for people with SMA:
More research is needed to determine the efficacy of these treatments. Assessments such as 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.
The HFMS consists of 20 items. Originally, pediatric SMA professionals developed the scale to evaluate the physical abilities of children with nonambulatory SMA (those with SMA who cannot walk unassisted). The scale’s creators chose these 20 items based on their ability to measure the physical functioning of children with both SMA type 2 and 3. Now, the HFMS is used for people of all ages who have type 2 or 3 SMA.
This test is administered by a physical therapist (physiotherapist). This specialist asks the person being evaluated to perform activities while standing, both supported and not supported. The physiotherapist then grades the execution and quality of the person’s movement. If the person is unable to execute 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. Forty is the highest score that can be achieved on the original HFMS.
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 HFMS was designed in 2003 for children with SMA type 2 and 3. Since that time, there have been additions to the scale. Other versions of the assessment also have been developed.
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.
The Hammersmith Functional Motor Scale Expanded 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 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.
In 2014, the HFMS and other SMA functional scales came under criticism for how accurately they measured physical abilities, their scoring, and their reliability, among other criticisms. Recommendations were made to revise the scales.
A consortium of SMA professionals met and reviewed the scales with the goal of enhancing the original assessment. The Revised Hammersmith Scale was designed by these SMA professionals. This scale has 36 items with a maximum score of 69. It includes two timed tests to evaluate strength and includes references to motor milestones from the World Health Organization.
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