In Spinal Muscular Atrophy, What Factors Influence Pain in Which Patients?
—Pain is common among patients with spinal muscular atrophy, but the prevalence among age groups is unknown. This study unveiled a link between several clinical characteristics and pain.
According to a new study, pain is common across all age groups of patients with spinal muscular atrophy (SMA) and is associated with female sex and a history of surgery for scoliosis.1
Many patients with neuromuscular disorders live with chronic pain.2 For example, a 2022 study found that hip pain was reported by 58% of patients with SMA.3 Hip pain in that study was associated with hip dislocations, hip contractures, surgery for scoliosis, and obesity.
In an interview with 澳门老奇人论坛, Leonie Steiner, PhD, of the Division of Neuropediatrics, Development and Rehabilitation, Bern University Hospital, University of Bern, Switzerland, and first author of the new study, said, 鈥淐hronic pain is an important factor for quality of life and can have an impact on participation in daily activities.鈥�
Dr. Steiner added, 鈥淔or patients with spinal muscular atrophy specifically, the literature regarding pain prevalence is very scarce.鈥�
In addition, few studies on pain in SMA have included children and adolescents. In these, pain was reported in 41% of patients with SMA type 2, 43% of patients of all types under age 18, and 71% of patients of all types aged 12-18 years.4-6 However, it is unclear whether the prevalence of pain differs between children, adolescents, and adults, as individual studies have not separately compared children and adolescents, for example.6
Because of the limited data, Dr. Steiner and her research group leader, Andrea Klein, MD, and colleagues initiated the new study of national registry data patients with SMA in Switzerland.
鈥淲e aimed to investigate the prevalence of chronic pain in children, adolescents, and adults with SMA, and secondly, we aimed to investigate its association with clinical characteristics, such as scoliosis, contractures, ambulation status, SMA type, and sex,鈥� Dr. Steiner explained.
Analyzing Swiss data
The Swiss Registry for Neuromuscular Disorders contains prospective data from patients with SMA and other NMDs beginning in 2008. In addition to clinical data, the registry contains patient responses at follow-up visits to queries regarding chronic pain in the previous 3 months.1
Data from all patients in the registry with SMA who had pain information through 2023 were analyzed. Because patients have multiple follow-up visits over time, a single patient could be included in more than one age group. Patients who died or who had no information about pain were excluded. Multivariable logistic regression was used to determine which characteristics were associated with the odds of having chronic pain.1
Patient characteristics
Out of 162 patients with SMA in the registry, pain data were available for 141 (86.5%). These 141 patients had 987 follow-up visits.1
Among the study population, 43% were female. The median age was 18 years (range, 1-66).1
Twenty-eight (19.9%) patients had SMA type 1, 59 (41.8%) had SMA type 2, 51 (36.2%) had SMA type 3, and 3 (2.1%) had unclassified SMA.1
Most patients had scoliosis (75.8%) and contractures (63.8%). A total of 30.5% could not sit, 50.4% could sit, and 19.2% could walk.1
Chronic pain during the previous 3 months was reported by 55 (39%) patients at least one follow-up visit, most often in the hips, back, and legs. Pain was reported by 32 (48%) adults, 16 (62%) patients aged 12-18 years, 11 (39%) patients aged 6-11 years, and four (10%) patients under 6 years.1
The use of pain medication was more common in younger patients. Among patients aged 12-18 years who reported pain, 81.8% took pain medication, as did 3 out of 4 patients under 6 years. Among adults, 44.8% of patients with pain took pain medication.1
Associations with pain
The investigators conducted multivariable regression analysis to determine the association between pain and patients and clinical characteristics. They excluded patients under the age of 6 (n=42) because disease-modifying therapies became available in Switzerland in 2017. Thus, these patients have had a different clinical course than older patients.1
The patient and clinical factors assessed for association with pain were age, sex, SMA type, mobility level, wheelchair use, contractures, and scoliosis. This analysis showed that pain was associated with female sex (odds ratio [OR], 3.27; (95% confidence interval [CI], 1.14-9.37; P=.028]. Scoliosis with surgery compared with no scoliosis was also associated with increased odds of pain (OR, 10.1; 95% CI, 1.53-11.0; P=.016). Scoliosis without surgery was not associated with increased odds of pain.1
Need for clinician awareness
Although SMA is rare, the investigators were able to study the majority of patients in Switzerland. 鈥淎lmost the whole SMA population in Switzerland was investigated, which was only possible due to the NMD registry in Switzerland with all needed information available,鈥� said Dr. Steiner. 鈥淭he demographics of the study population (N=141) were comparable to the entire registered SMA population in Switzerland (N=162) and thus represent an excellent study sample.鈥�
One implication of the study is that clinicians should be aware that chronic pain in SMA may vary across the lifespan. 鈥淚t is important to acknowledge that the prevalence of chronic pain is different for different age groups, with the highest prevalence rate present in adolescents (62%) and the lowest for children under 6 years of age (9%),鈥� said Dr. Steiner.
The investigators noted in their paper that the high prevalence of pain in adolescents in their study is comparable to that of a previous study of patients with SMA or Duchenne and Becker muscular dystrophy. Another similar finding between the studies was the high prevalence of pain in patients with a history of spinal surgery.5
Dr. Steiner said, 鈥淢anaging pain in patients with SMA begins with the recognition that there are predictable etiologies leading to pain in SMA and investigating them during each medical visit is important to implement interventions early.鈥� She added, 鈥淎wareness should be heightened among health care providers that pain can be an important issue in patients with SMA.鈥�
The investigators wrote that limitations were the potential for underreporting of pain, the lack of information about the functional impact of pain, and the lack of information about treatments that may influence pain.1
To address these limitations, the team has been considering future studies to explore the factors behind pain in SMA. 鈥淣ext steps would be to investigate the effect of some variables that were not included, such as different treatments to reduce pain (eg, physiotherapy focusing on pain), psychological state, the effect of concomitant medication, and participation in activities,鈥� said Dr. Steiner.
They believe another focus should be on direct patient reports. 鈥淐hronic pain was reported by the clinician and was not directly reported by the patient,鈥� said Dr. Steiner. 鈥淧ain might, therefore, be underreported, and using questionnaires directed to the patients themselves would be better for future research. These additional aspects would add context and deepen the interpretation of our results.鈥�
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