The data provided by one of the major publications on the incidence of GO [
20] did not include age-specific intervals. However, the authors stated that “age distribution differed in GO and Graves’ hyperthyroidism, with GO being less than 2% of Graves’ hyperthyroidism at age 20–40 year and 8% at age 40–60 year.” We therefore estimated age and sex-specific incidences derived from [
20] and used them to calculate prevalence (Table
2).
Table 2
Estimated age and sex-specific incidences derived from Laurberg et al. [
20]. These figures were used to calculate prevalence of GO
0–20 | 2.7 | 0.005 |
20–40 | 6.7 | 0.014 |
40–60 | 26.7 | 0.054 |
>60 | 13.4 | 0.027 |
This is the only study which directly assessed the incidence of GO in a large European population prospectively and included new cases between 1992 and 2011, based on approximately 8.9 million person-years of observation [
20]. The incidence of moderate-to-severe GO was 0.161/10,000/year with a median age at onset of 50 years [
20]. Mild cases of GO were not included due to difficulties in defining mild GO in large-scale epidemiological surveys. Distinguishing mild GO from normality and from the transient ocular effects of thyrotoxicosis of any cause, can be a challenge, especially if multiple observers are involved with variable degrees of expertise. In recent cross-sectional studies from secondary or tertiary centres, conducted by highly trained observers and with well-defined criteria for GO, about 65% of all cases of GO were found to have mild GO, and about 2% sight-threatening, disease [
11,
16]. We assumed that the cases of mild GO which were excluded by Laurberg et al. [
20], accounted for 2/3 (65%) of all cases of GO. Hence, the adjusted figure for incidence of all grades of severity of GO, based on the above studies [
11,
16,
20], is 0.483/10,000/year (incidence of moderate-to-severe disease 0.161 multiplied by 3, in view of the fact that it represents 1/3 of all cases = 0.483). The data published by Laurberg et al. [
20] are unclear as to whether sight-threatening GO was included within the moderate-to-severe category. We therefore used the frequency of sight-threatening GO of 2% cited by other publications [
11,
16] to calculate the prevalence of sight-threatening GO from data by [
20]. Using the approach described in “methods” the prevalence of GO is estimated to be 8.97/10,000 population. It can be further broken down to mild (5.83/10,000), moderate-to-severe (2.96/10,000) and sight-threatening GO (0.18/10,000) (Table
3a).
Table 3
Estimated prevalence of GO and variants of GO. (a) shows prevalence by severity and (b) for clinical variants (all grades of severity)
(a)
|
All cases of GO | 8.97 | - | |
15.48 | | |
Mild GO | 5.83 | 65.0% | |
11.03 | 72.8% | |
Moderate-to-severe | 2.96–4.45 | 33.0–29.4% | |
Sight-threatening | 0.18 | 2.0% | |
(b)
|
Euthyroid/hypothyroid GO | 0.02–1.10 | 0.2–11.0% | |
GO associated with dermopathy | 0.15 | 1.5% | |
GO associated with acropachy | 0.03 | 0.3% | |
Asymmetrical GO | 1.00–5.00 | 10.0–50.0% | |
Unilateral GO | 0.50–1.50 | 5.0–15.0% | |