Current tools for measuring motor function in spinal muscular atrophy (SMA) are helpful, but they can sometimes miss issues involving bulbar function, fatigability, quality of life, and daily functioning. New tools are being created to better track some of these important changes.

SMA progression is characterized by a progressive weakness that generally affects the lower limbs before the upper limbs, but there are exceptions, particularly in patients with the most severe disease. Before the current treatment era, historical phenotypes were typically defined based on the age of onset and the highest gross motor milestone achieved. Now, with treatment, the focus is more on the patient’s genotype, which is a predictor of disease severity, plus their current functional status. Patients with SMA are now classified as being sitters, nonsitters, or ambulatory rather than as specific types.

Many of the assessment scales used in clinical practice for SMA have been validated in clinical trials, can help monitor disease progression, and provide standardized measures across centers so that we can collectively communicate with each other about how our patients are doing. Scales used in clinical trials and in clinical practice are the Children’s Hospital of Philadelphia Infant Test of Neuromuscular Disorders for infants, the Hammersmith Functional Motor Scale or its expanded version for slightly older patients, and the Revised Upper Limb Module for SMA for ambulatory and nonambulatory individuals. Because we have the treated phenotypes, we also incorporate norm-referenced scales that are designed for patients without SMA, including the Hammersmith Infant Neurological Examination, the Bayley Scales of Infant and Toddler Development, and the World Health Organization (WHO) gross motor milestones outlined in the WHO Multicentre Growth Reference Study.

However, many assessment scales may not capture important symptoms in older patients or in those with more severe stages of SMA, such as fatigability and volume of voice. Therefore, newer clinical tools are being evaluated in patients with SMA that include domains for bulbar function, communication, and fatigability. An international, multidisciplinary group of clinicians developed a bulbar assessment scale specifically for SMA that evaluates the domains of oral intake status, oral facial structure and motor strength, swallowing physiology, voice and speech, and fatigability. Another new scale to be aware of is the Spinal Muscular Atrophy Functional Rating Scale, which provides more patient and caregiver input on functional independence with activities of daily living that are not captured as well by the current motor scales. So, there are some newer scales in development that evaluate areas that we have not typically been capturing for patients with SMA, such as oral motor function, quality of life, fatigue, and other aspects of daily living.