Development and validation of the patient-reported “Facial Function Scale” for facioscapulohumeral muscular dystrophy

Figures & data

Table 1. Results of Rasch analyses.

Analysis	Item location (mean, SD)	Item fit residual (mean, SD)	Person location (mean, SD)	Person fit residual (mean, SD)	Item trait interaction df; p value	PSI	Unidimensionality t-test % [95%CI]	Floor effect^a
Initial (33 items)	0.00 ± 0.99	–0.32 ± 1.23	–2.27 ± 1.29	–0.27 ± 0.91	66; 0.019	0.94	13.3% [9.3–17.3]	5%
After reordering thresholds (33 items)	0.00 ± 0.95	–0.34 ± 1.25	–1.86 ± 1.45	–0.29 ± 0.87	66; 0.037	0.94	10.6% [6.6–14.6]	5%
Semi-automated analysis (27 items)	0.00 ± 0.97	–0.31 ± 1.16	–1.82 ± 1.45	–0.25 ± 0.88	54; 0.166	0.92	8.0% [4.0–12.1]	6%
Final (25 items)	0.00 ± 0.99	–0.33 ± 1.16	–1.84 ± 1.45	–0.27 ± 0.87	50; 0.678	0.92	6.3% [2.3–10.4]	7%

PSI: person separation index; SD: standard deviation; CI: confidence interval.

^a Proportion of participants achieving the lowest score possible.

Table 2. Final Rasch-built “Facial Function Scale”.

	Often (2)	Sometimes (1)	Never (0)
1. Do you suffer from dry eyes or from the feeling of grains of sand in your eyes?
2. Do your eyelids get fatigued during the day?
3. Do you experience difficulty swallowing drinks?
4. Do you choke while eating?
5. Do you experience difficulty with the control of your saliva (does saliva run out of your mouth or do you choke on saliva)?
6. Do you spill food from your mouth?
7. Does your face get fatigued during eating?
8. Does eating take longer due to weakness of the muscles around your mouth?
9. Do you experience difficulty biting off foods?
10. Do you experience difficulty chewing foods?
11. Are you afraid of choking when eating and/or drinking?
12. Does your face get fatigued during speaking?
13. Is your speech more slurred due to facial weakness?
14. Does your face get fatigued during laughing?
15. Do others think you come across as angry or indifferent?
16. Do others ask you if you are having a good time?
17. Do you feel like you are misunderstood due to changed facial expressions?
18. Are social situations less satisfactory to you due to facial weakness or changed facial expressions?
19. Does facial weakness reduce your self-confidence?
	Without difficulty (0)		With difficulty (1)
20. Are you able to wink?
21. Are you able to whistle?
22. Are you able to blow up a balloon?
23. Are you able to drink through a straw?
24. Are you able to smile?
25. Are you able to swallow with your lips put together?

The presented raw scores in this table should be summed to obtain a total score, that is then transformed into an interval score (Table 3, nomogram) for proper application. Permission to use this scale should be obtained through the authors.

Figure 1. Distribution of facial function evaluation (ability location) as assessed with the Facial Function Scale and threshold map of the final 25-item scale.

Upper section contains a bar chart that shows that the distribution of facial function evaluation of the 119 FSHD patients as assessed with the Facial Function Scale. There is a small floor and ceiling effect, and minor gaps of less than 1 logit between person abilities at both ends of the scale. Lower section shows a threshold map ordering the final 25 items of the Facial Function Scale from the most challenging item (blowing up a balloon) to the least challenging item (fatiguing of the face during eating).

Table 3. Nomogram.

FFS raw score	Rasch person location (logits)	Centile metric
0	–4.69	0
1	–3.81	9
2	–3.23	15
3	–2.83	19
4	–2.52	23
5	–2.26	26
6	–2.03	28
7	–1.83	30
8	–1.65	32
9	–1.48	34
10	–1.32	35
11	–1.18	37
12	–1.04	38
13	–0.91	40
14	–0.79	41
15	–0.67	42
16	–0.55	44
17	–0.44	45
18	–0.33	46
19	–0.22	47
20	–0.11	48
21	–0.01	49
22	0.10	51
23	0.20	52
24	0.30	53
25	0.41	54
26	0.51	55
27	0.62	56
28	0.73	57
29	0.84	58
30	0.96	60
31	1.08	61
32	1.20	62
33	1.33	64
34	1.47	65
35	1.62	67
36	1.78	68
37	1.96	70
38	2.15	72
39	2.37	75
40	2.63	77
41	2.93	81
42	3.33	85
43	3.90	91
44	4.72	100

Nomogram for translation of summed raw scores of the final Facial Function Scale (FFS, range 0–44) to an estimate of the Rasch person location (logits) and a more convenient centile metric scale, most suited for routine use (range 0–100).

Data availability statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.