Spinal Muscular Atrophy (SMA)

Spinal muscular atrophy (SMA) may place people at a higher risk of developing comorbidities. Generally, spinal muscular atrophy comorbidities are more severe depending on the overall severity of the disease.

SMA comorbidities can affect many organs and systems including skeletal muscle, the heart, kidney, liver, pancreas, spleen, bone, connective tissues, and the immune system.

Muscular and Skeletal Comorbidities

The most common comorbidity of the skeletal system in people with SMA is scoliosis.¹ It mostly affects patients with SMA type 1 and 2, and may also affect those with SMA type 3.² Scoliosis develops because the muscles on either side of the spine are too weak to support it. The spinal abnormality can adversely affect respiratory function, balance, and the movement of the arms.

People with SMA may also develop kyphosis or Iordosis, which can cause pain and limit range of motion.¹

Another comorbidity people with SMA may develop is pelvic obliquity, which can lead to hip dislocations over time¹. 

Another comorbidity common in people with SMA is joint contracture in the lower and upper extremities, which limits movement and causes pain.^3,4

Some people with SMA may also develop jaw problems and may find it difficult to open their mouths.⁵ 

Comorbidities Affecting the Respiratory System

Chronic and acute respiratory failure is common in patients with SMA, especially those with a more severe disease course such as SMA type 1 or 2.⁶ SMA results leads to very weak intercostal muscles in the context of a relatively strong diaphragm.⁷

Recurrent respiratory infections are also common in patients with SMA due to compromised respiratory function and the inability to cough due to muscle weakness.⁷

Some patients may experience aspiration pneumonia, where gastric content is inhaled into the lungs, causing chest infections.⁸ Scoliosis can also contribute to difficulty breathing because it can distort the shape of the chest.

Comorbidities Affecting the Cardiovascular System

Patients with SMA type 1 may have congenital heart problems such as atrial or ventral septal defects, hypoplastic left heart syndrome, and cardiac outflow tract abnormalities.⁹ 

Patients with SMA type 1, 2, and 3 can also experience heart arrhythmia,⁹ as well as hypertension.¹⁰

Other SMA Comorbidities

Patients with SMA may develop diabetes mellitus.¹⁰ A mouse model of SMA exhibits a large predominance of glucagon-producing alpha cells and diminished insulin-producing beta cells, resulting in fasting hyperglycemia, hyperglucagonemia, and glucose resistance.¹¹ Similar findings were documented in humans with SMA.¹¹

Management and Treatment of SMA Comorbidities

Treating or managing SMA comorbidities can improve patients’ quality of life. 

Scoliosis or other spinal disorders may be managed using braces to hold the spine in place and slow their progression.² Physiotherapy may also help slow the progression of scoliosis as it aims to strengthen specific muscles and relax the joints.¹²

However, the most common treatment for scoliosis is surgery[link to SMA surgery page].² The main surgery is the sublaminar band technique, where rods are inserted on either side of the spine and plastic or acrylic bands are attached between the vertebrae. Because most patients are still growing when they need scoliosis surgery, the bands usually need to be adjusted every 6 to 12 months through minor surgeries to allow for growth.

Another type of scoliosis surgery is a spinal fusion that can be performed in patients who are no longer growing. With this procedure, individual vertebrae are joined together using pieces of bone taken from the bone around the pelvis.

Finally, a newer surgical approach that uses magnetic control rods has been shown to be beneficial in correcting scoliosis in children with SMA. The rods can allow the spine to grow and adjustments to be made without further surgery. 

Hip dislocations may also need to be treated with surgery to reduce pain and improve balance.¹

Physiotherapy and occupational therapy can help reduce joint contracture, as can splints and braces. 

Respiratory comorbidities can be treated with noninvasive or invasive respiratory support or respiratory therapy.¹³ Noninvasive or invasive respiratory ventilation can be used judiciously to support respiratory function. 

In respiratory therapy, a pulmonologist or respiratory care therapist teaches patients airway clearance techniques to help strengthen coughing. Some patients with severe cardiac arrhythmia may need pacemaker implantation.¹⁴

Reviewed by Michael Sapko, MD on 7/1/2021

References

1. Scoliosis in SMA. SMA Foundation. Accessed June 1, 2021.
2. Scoliosis in SMA. Spinal muscular atrophy UK. Accessed June 1, 2021.
3. Fujak A, Kopschina C, Gras F, Forst R, Forst J. Contractures of the lower extremities in spinal muscular atrophy type II. Descriptive clinical study with retrospective data collection. Ortop Traumatol Rehabil. 2011;13(1):27-36. doi:10.5604/15093492.933792
4. Fujak A, Kopschina C, Gras F, Forst R, Forst J. Contractures of the upper extremities in spinal muscular atrophy type II.  Ortop Traumatol Rehabil. 2010;12(5):410-9. 
5. Van Bruggen HW, van den Engel-Hoek L, van der Pol WL, de Wijer A, de Groot IJM, Steenks MHl. Impaired mandibular function in spinal muscular atrophy type II. J Child Neurol. 2011;26(11):1392-1396. doi:10.1177/0883073811407696 
6. Prior TW, Leach ME, Finanger E. Spinal muscular atrophy. In: Adam MP, Ardinger HH, Pagon RA, et al, eds. GeneReviews^®. University of Washington, Seattle; 2000. Accessed June 1, 2021.
7. Schroth MK. Special considerations in the respiratory management of spinal muscular atrophy. Pediatrics. 2009;123 Suppl 4:S245-249. doi:10.1542/peds.2008-2952K
8. Chen YS, Shih HH, Chen TH, Kuo CH, Jong YJl. Prevalence and risk factors for feeding and swallowing difficulties in spinal muscular atrophy types II and III. J Pediatr. 2012;160(3):447-451.e1. doi:10.1016/j.jpeds.2011.08.016 
9. Wijngaarde CA, Blank AC, Stam M, Wadman RI, van den Berg LH, van der Pol WL. Cardiac pathology in spinal muscular atrophy: a systematic review. Orphanet J Rare Dis. 2017;12:67. doi:10.1186/s13023-017-0613-5
10. Darbà J, Marsà A. Patient characteristics and hospitalisation costs of spinal muscular atrophy in Spain: a retrospective multicentre database analysis. BMJ Open. 2019; 21;9(11):e031271. doi:10.1136/bmjopen-2019-031271
11. Bowerman M, Swoboda KJ, Michalski JP, et al. Glucose metabolism and pancreatic defects in spinal muscular atrophy. Ann Neurol. 2012;72(2):256–68. doi:10.1002/ana.23582
12. Living with SMA. Spinal Muscular Atrophy Clinical Research Center. Accessed May 31, 2021. 
13. Breathing basics: respiratory care for children with spinal muscular atrophy. Cure SMA. Accessed June 3, 2021.
14. Palladino A, Passamano L, Taglia A, et al. Cardiac involvement in patients with spinal muscular atrophies. Acta Myol. 2011;30(3):175-178. doi:10.1016/j.nmd.2011.06.902

Reviewed by Michael Sapko, MD, on 7/1/2021.

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Ozge Ozkaya, MSc, PhD

Özge’s background is in research; she holds a MSc. in Molecular Genetics from the University of Leicester and a PhD. in Developmental Biology from the University of London. Özge worked as a bench scientist for six years in the field of neuroscience before embarking on a career in science communication. She worked as the research communication officer at MDUK, a UK-based charity that supports people living with muscle-wasting conditions, and then a research columnist and the managing editor of resource pages at BioNews Services before joining Rare Disease Advisor.