Potential Complications of SMA

Poor weight gain with growth failure, restrictive lung disease, scoliosis, joint contractures, and sleep difficulties are common complications of SMA in those who receive supportive care only. At this time, it is unknown what long-term complications may arise in individuals who receive early and/or presymptomatic targeted treatment.

Nutrition/gastrointestinal

• Bulbar dysfunction is universal in individuals with SMA I; the bulbar dysfunction eventually becomes a serious problem for persons with SMA II and only very late in the course of disease for those with SMA III.

• Gastrointestinal issues may include constipation, delayed gastric emptying, and potentially life-threatening gastroesophageal reflux with aspiration.

• Growth failure can be addressed with gastrostomy tube placement as needed (see Management).

• Nonambulatory individuals with SMA II and III are at risk of developing obesity [Mercuri et al 2018].

Respiratory. Children with SMA I and II (and more rarely, type III) who are treated with supportive care only have progressive decline in pulmonary function due to a combination of weak respiratory muscles, reduced chest wall and lung compliance, and a reduction in alveolar multiplication [Chng et al 2003].

• Respiratory failure is the most common cause of death in SMA I and II.

• Decreased respiratory function leads to impaired cough with inadequate clearance of lower airway secretions, hypoventilation during sleep, and recurrent pneumonia.

• Noninvasive ventilation, such as BiPAP, and airway clearance techniques are commonly used to improve respiratory insufficiency in those with SMA (see Management).

Orthopedic. Scoliosis, hip dislocation, and joint contractures are common complications in individuals with SMA. Scoliosis is a major problem in most persons with SMA II and in half of those with SMA III. With supportive care only:

• Approximately 50% of affected children (especially those who are nonambulatory) develop spinal curvatures of more than 50 degrees (which require surgery) before age ten years;

• Later in the disease course, nonambulatory individuals can develop thoracic kyphosis [Mercuri et al 2018];

• Progressive scoliosis impairs lung function and if severe can cause decreased cardiac output [Chng et al 2003].

Use of the vertical expandable prosthetic titanium rib is a possible treatment for severe scoliosis (see Management).

Metabolic. An unexplained potential complication of SMA is severe metabolic acidosis with dicarboxylic aciduria and low serum carnitine concentrations during periods of intercurrent illness or prolonged fasting [Kelley & Sladky 1986].

• Whether these metabolic abnormalities are primary or secondary to the underlying defect in SMA is unknown.

• Although the etiology of these metabolic derangements remains unknown, one report suggests that aberrant glucose metabolism may play a role [Bowerman et al 2012].

• Prolonged fasting should be avoided (see Agents/Circumstances to Avoid).

References

" GeneReviews", National Library of Medicine, 2023, https://www.ncbi.nlm.nih.gov/books/NBK1352/#sma.Resources. Accessed 7/4/2023.