In this retrospective study, high rates of women with autoimmune abnormalities (36.2%) and with decreased BMD in DEXA (60.4%) were observed. Once more, these findings underline the overall importance of POI, which exceeds amenorrhea and sterility by far. Notably, POI has been claimed a “serious chronic disease with far reaching effects on physical and emotional health” [22]. The involvement of a care manager should be considered not only to ensure comprehensive care (doctors, nurses, psychologists, etc.) but also to guarantee a better overall satisfaction in terms of a collaborative team. This would improve self-management skills and, thus, patient empowerment, as well as provide the necessary advice and information. A better control of the disease and improved clinical parameters would be desirable [23].
Concerning the high rate of abnormal DEXA results (about 60%), the majority of patients showed osteopenic DEXA values (48.3% of all women), whereas osteoporotic values were found less frequently (12.1% of all women). However, it has been demonstrated that the majority of fractures occur in an osteopenic state [24]. In addition, there is evidence that low BMD predicts progression to osteoporosis later in life. Less than 10% of postmenopausal women with normal bone density or mild osteopenia develop osteoporosis within a period of 15 years, women with moderate osteopenia within 5 years, whereas women with advanced osteopenia show osteoporosis within 1 year [25]. Therefore, the result is of high clinical relevance.
In literature, the rate of POI women with an abnormal BMD differs widely. Possible explanations would be different definition criteria for abnormal DEXA results. On the other hand, bone density is probably dependent on age in POI patients. A large cross-sectional study demonstrated that among 442 POI patients, 15% had a Z-Score below the expected range of age (defined as <−2) and 8% were already in an osteoporotic state (<−2.5). The women’s median age was about 29 years [8]. In contrast, Anasti et al. reported that in karyotypically normal POI patients, 67% presented a femoral neck bone density more than one standard deviation below the mean of the reference group. This prevalence as well as the women’s median age of 33 years [7] were similar to our results. On the one hand, the cut-off criteria used to define an abnormal DEXA result might be considered of relevance. On the other hand, based on the studies cited above, one could hypothesize that the prevalence of abnormal DEXA results would increase with age. In our patient population, age closely failed to reach statistical significance (p = 0.054, Table 2), which might be due to the sample size.
One significant factor that was associated with a lower BMD in our data set was a longer duration of amenorrhea before DEXA measurement (Table 2). In our study patients had been amenorrhoic before DEXA evaluation for a median of 12 months. Hypothetically, amenorrhea could be seen as a sign for a more severe POI condition as well as longer lasting estrogen deficiency. In line with our results, it has already been reported that POI women who had had a 1-year delay of diagnosis after the onset of symptoms (i.e., menstrual irregularities) showed lower BMD levels than patients who were diagnosed earlier [8]. Both observations, namely the negative influence of advanced age and the delay of diagnosis on BMD, suggest that early detection seems important to establish hormone replacement therapy as soon as possible to avoid BMD decrease [26]. Furthermore, our multivariate model demonstrated a lower BMI as a risk factor for decreased BMD. It is well known that a BMI <18.5 kg/m2 is linked to an increased risk of fracture. Within eutrophic ranges, BMI seems to have a protective role on BMD, but this effect decreases steadily towards obesity. Previous observations indicated a nonlinear relationship between BMI and BMD [27, 28]. Notably, in our study cohort, the mean BMI was 21.4 kg/m2, which is in the range of normal weight.
One new and important finding is the association between the presence of autoimmune abnormalities and low bone density in women with POI. It obviously supports the assumption that autoimmunity might represent an important driver in pathogenic bone loss [15]. Decreased BMD has been found in patients with SLE [12], chronic thyroiditis [13] and autoimmune hepatitis [14] in previous studies. Although declines in BMD in patients with SLE might also be due to the SLE-related glucocorticoid treatment, several studies have pointed out that autoantibodies were able to induce osteoclast differentiation and activation and to alter bone mineral content. However, the exact mechanisms are not yet clear and deserve further exploration [15]. Moreover, it has been suggested that thyroid autoimmunity was a potential marker of higher fracture risk in patients with subclinical hypothyroidism [29, 30].
It is estimated that autoimmune disease is present in approximately 10–40% of patients with POI [9, 11]. The prevalence of about 36% found in our data set is within that range. A few studies demonstrated a prevalence of autoimmune conditions similar to our study: Doldi and colleagues [16] observed organ-specific autoantibodies in 44% of women with POI. Notably, in our study, women with genetic abnormalities had already been excluded which might explain the high rate of patients with associated autoimmunity. However, Alper et al. [31] showed evidence of autoimmune disorders in 39% of chromosomally competent POI women which is also in line with our results.
In literature, thyroid disorders proved to be most frequently associated with POI (27%), followed by Addison disease (2.5%) and diabetes mellitus (2.5%) [31,32,33]. However, the rates differed widely. For example, in our analysis, POI women were screened using various antibodies and the most frequently found abnormalities were elevated serum levels of TPOAb (24.1%), TGAb (20.7%) and ENA subsets (5.2%). To the best of our knowledge, only one study evaluated comparable numbers of antibodies. Zhen et al. [11] reported that women with POI had significant higher levels of PR3 and Jo-1 antibodies; whereas, thyroid microsomal antibodies, ANAs and ENA subsets were similar between POI patients and healthy controls. Nevertheless, thyroid antibodies are most often associated with POI. The highest rate had been reported by Pogacnik et al. [34] who had excluded POI patients with infectious, iatrogenic or genetic causes and found that 50% of POI women were positive for TG antibodies.
It should be noted that it seems questionable whether antibody screening in POI patients would be useful. According to the ESHRE Guideline Group on POI, screening for 21OH-Ab/ACA and TPOAb should be performed if unknown etiology or an immune disorder is suspected [3]. Since there is no possibility for non-invasive testing for the diagnosis of an autoimmune etiology, Kirshenbaum et al. [35] recommended the screening for the most common autoantibodies in women with POI, i.e,. steroid cell antibodies, anti-ovarian antibodies and anti-thyroid antibodies. Both studies suggested to include thyroid antibodies as part of a clinical routine screening in POI patients, which were also evaluated in our study and showed significant results.
The weakness of our study is shown by the lack of data collection concerning adrenal cell antibodies, anti-ovarian antibodies and steroid cell antibodies. Thus, important markers for autoimmune polyendocrine syndrome types I and II are missing. Notably, the parameters collected were part of an autoimmune panel available in clinical routine. Thus, we can neither provide a detailed rationale for every marker chosen, nor data on other probably important parameters. We consider this circumstance a major study limitation, although it seems worth pointing out that several other antibodies were evaluated and these rather new results should add to the knowledge about autoimmunity in POI. Moreover, the study is limited by its retrospective design and the small sample size. Due to the retrospective nature of our study, we cannot provide data on autoimmunity-related symptoms, which we consider unfortunate. Nevertheless, we did not only focus on autoimmune screening in POI patients, but also focused on DEXA findings.