Clinical Presentation of SMA by Type
SMA is categorized into subtypes based on age of onset and highest motor milestone achieved. The most common three types in children present as follows:
TYPE 1
(SEVERE/MOST COMMON FORM)
Symptom onset <6 months
- Progressive hypotonia
- Typical supine position is bent elbows and frog legs
- Difficulty lifting extremities against gravity
- Rapid paradoxical breathing or belly breathing
- Bell-shaped chest
- Poor head control / head lag
- Bulbar weakness / dysphagia
- Developmental regression
- Never sits
TYPE 2
Symptom onset 6 to 18 months
- Progressive hypotonia
- Difficulty lifting extremities against gravity
- Possible paradoxical breathing or belly breathing
- Possible bell-shaped chest
- Tongue fasciculations
- Absent deep tendon reflexes
- Developmental regression
- Delayed sitting and never walks unaided
Type 3
Symptom onset 1.5 to 10 years
- Progressive hypotonia
- Muscle tremor
- Fatigue with exertion and frequent falls
- Gower’s sign, Trendelenburg gait, hyperlordosis, and foot overpronation
- Developmental regression
- Delayed walking
Multiple effective treatments approved by the U.S. Food and Drug Administration (FDA) have dramatically changed the natural history of SMA. Promptly evaluate for SMA upon suspicion in clinic. Genetic testing is required to confirm SMA. Rapid response can save and dramatically improve a child’s life.
SMArt Moves Professionals’ Proof Points
Historically, healthcare professionals have been slow to refer a child for concerns about motor delays. In part, SMA is a rare disease and an SMA diagnosis was once perceived as dismal, prior to the availability of the first FDA-approved treatment for SMA in 2016. There are now multiple FDA-approved treatments for SMA, and additional treatments in development or in clinical trials. With the availability of these life-altering SMA treatments, the timing of administration is crucial.
- Early treatment, within the first few months after exhibiting SMA symptoms, will show significant improvements. SMA treatment started after that crucial early window can still result in benefit, but their health outcomes and improvements may not be as great compared to children treated at the earliest onset of the disease.
- Most children are not being diagnosed as early as possible, even when presenting tell-tale symptoms.
- Most parents instinctually know something is wrong but are not exactly sure if these developmental delays are serious, or they may be in denial. If a healthcare professional initially dismisses concerns, parents are generally not prepared to prompt further conversations to drive a thorough evaluation.
- Doctors often suggest a “wait-and-see” approach in response to a child’s motor developmental delays and may not be attune to the nuances of diagnosing SMA. They may not know the urgency required to maximize the effectiveness of available SMA treatment.
We hope this information will help you make informed decisions about diagnosing SMA and change the outcome for so many young children and their families.
Additional Facts & Resources
References:
Finkel RS, Mercuri E, Darras BT, et al. Nusinersen versus Sham Control in Infantile-Onset Spinal Muscular Atrophy. N Engl J Med. 2017;377(18):1723–1732. doi:10.1056/NEJMoa1702752 https://www.nejm.org/doi/full/10.1056/NEJMoa1702752
Mendell JR, Al-Zaidy S, Shell R, et al. Single-Dose Gene-Replacement Therapy for Spinal Muscular Atrophy. N Engl J Med. 2017;377(18):1713–1722. doi:10.1056/NEJMoa1706198 https://www.nejm.org/doi/10.1056/NEJMoa1706198
Mercuri E, Darras BT, Chiriboga CA, et al. Nusinersen versus Sham Control in Later-Onset Spinal Muscular Atrophy. N Engl J Med. 2018;378(7):625–635. doi:10.1056/NEJMoa1710504 https://www.nejm.org/doi/full/10.1056/NEJMoa1710504
De Vivo DC, Bertini E, Swoboda KJ, et al. Nusinersen initiated in infants during the presymptomatic stage of spinal muscular atrophy: Interim efficacy and safety results from the Phase 2 NURTURE study. Neuromuscul Disord. 2019;29(11):842–856. doi:10.1016/j.nmd.2019.09.007 https://www.nmd-journal.com/article/S0960-8966(19)31127-7/fulltext
