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Survival rates of patients with the rare genetic disease known as spinal muscular atrophy (SMA) have been grim at best. While these patients are faced with a reduced life expectancy, newer disease-modifying therapies (DMTs) have given hope to people with this prognosis.

These medications have brought new interest to patients鈥� health-related quality of life (HRQoL), given the disabling effects of SMA, including progressive muscular atrophy and weakness. To expand on this topic, the authors of a recently published article in Quality of Life Research investigated HRQoL鈥攚hich they described as 鈥渢he individual鈥檚 perception of the impact of health and illness on physical, mental, and social aspects of life鈥濃�攊n adults with SMA.¹

Measuring quality of life, 3 ways

This cross-sectional cohort study used 3 of the most common measures of HRQoL: the EQ-5D-5L, the Health Utilities Index Mark III (HUI), and the 36-item Short Form Health Survey (SF-36). Between June and September 2021, a time period when DMTs were available to patients with SMA, 82 patients from a German SMA patient registry completed an online questionnaire on their demographic and clinical characteristics, as well as the 3 scales/scoring systems of HRQoL mentioned above. During the study, more than 3 out of 4 (76%) patients were using DMTs, with a mean duration of 3 years.

The patients enrolled included non-sitters (9%), sitters (67%), and walkers (24%); of the total sample, 4% had SMA type I, 34% had type II, and 62% had type III. Non-sitters were defined as those requiring ventilatory and feeding support, whereas sitters and walkers had lesser degrees of impairment. The mean age of patients was 42 years, and 51% were female.

Degrees of impairment vary by subgroup

The authors were unsurprised with the results of the EQ-5D-5L, 鈥済iven the devastating clinical presentation and trajectory of SMA.鈥�¹ They went on to explain that 鈥渕ost participants experienced considerable problems with mobility, as well as self-care. Yet the impact of the progressive loss of motor skills on other domains of life varied across examined subgroups.鈥�¹

Specifically, for the EQ-5D-5L assessments, the estimated mean score for the total sample was 0.5135 (range 0.31 to 0.99). Results also revealed that <2% of patients were in the best possible health (equivalent to a score of 1.0000), and 0 patients were in the worst possible health (equivalent to a score of 鈥�0.6610). The mean EQ-VAS (visual analog scale) score was estimated at 69.71 (range 30 to 93) for non-sitters, 71.40 (range 10 to 100) for sitters, and 63.95 (range 10 to 96) for walkers.

Furthermore, for EQ-5D-5L measures, non-sitters reported moderate, severe, or extreme problems with mobility and self-care (100%), followed by usual activities (43%), pain/discomfort (29%), and anxiety/depression (29%). For sitters, the results were similar: mobility (96%), self-care (85%), usual activities (44%), pain/discomfort (18%), and anxiety/depression (13%). Walkers were understandably less affected with mobility (50%) than the other groups but had their own concerns, including those related to usual activities (40%), pain/discomfort (35%), self-care (25%), and anxiety/depression (15%).

Ambulation, dexterity are common problems

For the HUI measures, the mean score for the total sample was 0.3171 (range 鈥�0.24 to 0.97). In their study, the authors explained the results 鈥渟howed that compromised HRQoL in adults with SMA primarily was driven by problems with ambulation and dexterity,鈥�¹ with 89% of patients having difficulty with ambulation and 59% with dexterity. Pain was also a factor, with 62% of patients reporting it, as well as issues with vision (57%), emotion (50%), cognition (27%), speech (15%), and hearing (4%). 

For the third measure, SF-36, the mean Physical Component Summary and Mental Health Component Summary scores were 33.78 (range 9.92 to 53.10) and 53.49 (range 21.02 to 72.25), respectively. The mean SF-6D (short form, 6 dimension) score was 0.6308 (range 0.58 to 0.65). No patients reported being in the best or worst possible health (鈥渂est鈥� being equivalent to a score of 1.0000 and 鈥渨orst鈥� being equivalent to a score of 0).

Limitations and conclusions

The authors believe that their results 鈥渟uggest that some patients with severe SMA learn to cope with their disease and value their health state and HRQoL differently than members of the general population.鈥�¹

Limitations of the study鈥攁side from its cross-sectional design and reliance on self-reported data collected from questionnaires, the latter of which may have introduced recall bias鈥攊ncluded its length of time. However, the authors believe that the 4-week period avoided recall bias as well as fluctuating disease states that might not have represented a patient with SMA. Nevertheless, the shorter time period may also not have allowed for a more stable assessment of patients鈥� current HRQoL that a longer study would have shown.

Further, selection bias may have played a factor, as severely ill patients 鈥渨ith considerable motor impairment may not have been able to participate,鈥�¹ the authors explained. In addition, validity or suitability was not established for the instruments for measuring HRQoL, as that would have required a more comprehensive analysis.

Despite these limitations, the authors concluded that their findings show 鈥渃onsiderable impairment across a wide range of health dimensions, including but not limited to mobility, dexterity, pain, and emotional well-being. However, our results exhibit non-trivial variability between examined patient groups, as well as HRQoL tools, indicative of the heterogeneous presentation and trajectory of SMA.鈥�¹

Published: August 22, 2024