What is Adenomyosis?
Adenomyosis is a benign gynaecological disease characterised by invasion of the uterine muscle (known as myometrium in humans) by the endometrial tissue the uterus. The processes of invasion, inflammation and hypertrophy, or enlargement, of the myometrium can lead to a broad spectrum of symptoms [1]. Adenomyosis is a prevalent disease that can seriously compromise the reproductive health of women, especially adults of childbearing age [2].
Adenomyosis can have multiple symptoms including heavy menstrual bleeding, painful menses, chronic pelvic pain and infertility, though as many as one in three patients may ultimately be asymptomatic [3].
Causes of Adenomyosis
The pathogenesis of adenomyosis is not yet fully understood, but several hypotheses have been put forward. One, which suggests that adenomyosis arises from an invasive growth of endometrial cells into uterine muscle, holds that it is linked to opening an incision in the uterus (eg, in a caesarean delivery) or in normal uterine function [4, 5].
Another hypothesis is that uterine inflammation after birth can rupture the usual barrier between the cells that line the uterus, thereby causing adenomyosis [4, 5].
Further hypotheses point to increased endometrial tissue experienced during childhood and in the uterine wall as being a cause, while others propose that it is related to the stem cells in the myometrium or uterine muscle wall [4, 5].
It has also been proposed that adenomyosis may originate from metaplasia of ectopically displaced embryonic pluripotent Müllerian remnants or differentiation of adult stem cells [6].
Nevertheless, the disease only represents a set of explanatory hypotheses and collected anecdotes, since the biological mechanism behind adenomyosis has not been fully clarified.
What is Leiomyoma?
Leiomyomas (also known as uterine fibroids or myomas) are benign tumours originating from myometrium cells, the muscle layer of the uterus. They represent the most frequent benign tumour type in females of reproductive age, with an estimated prevalence of ~70% in this population [7]. Despite their benign nature, leiomyomas are often accompanied by considerable health issues such as heavy menstrual bleeding, pelvic pain, infertility and recurrent abortion [7].
Causes of Leiomyoma
While the precise causes of leiomyomas remain somewhat elusive, several risk factors have been implicated in their pathology. Genetic factors represent a major cause for the onset of hormone-dependent tumours, as mutations in the gene encoding the transcriptional coactivator MED12 have been identified as a major cause of uterine leiomyomas [8]. Nevertheless, the clinical and molecular characteristics of the familial vs sporadic forms can broadly differ because of the high heterogeneity of the disease and the several factors that can underlie tumorigenesis [9].
Hormonal factors are also important in the pathogenesis of leiomyomas. Ovarian steroid hormones, particularly oestrogen and progestogen, have been shown to mediate leiomyoma pathology through their gene regulatory mechanisms [10]. Hormonal exposure early in life during critical developmental periods may induce developmental reprogramming through epigenetic changes that become permanent in adulthood [7].
Environmental causes related to obesity are also associated with increased leiomyoma risk [9]. Growth factors, cytokines, chemokines and microRNAs all have been implicated as key regulators of SM leiomyoma growth [11].
Similarities and Differences Between Adenomyosis and Leiomyoma
Adenomyosis and leiomyoma, also known as uterine fibroids, are both common benign conditions of the uterus. They share some similarities but also have distinct differences.
Similarities
These two conditions, adenomyosis and leiomyoma, cause pelvic pain and heavy menstrual bleeding. When women have adenomyosis and leiomyoma, they have more severe pelvic pain than when women have leiomyoma alone [12, 13, 14].
Differences
There are, however, important differences between the two conditions. Women with adenomyosis are younger (mean age of 41.1 years vs 44.3 years) and more likely to have a history of depression (57.1% vs 24.7%) than those with leiomyoma [14].
A history of smoking and at least one delivery increases the chances of having adenomyosis [15]. What’s more, women with adenomyosis and leiomyomas tended to be lighter and have less fibroid burden than those with just leiomyomas alone [13].
Furthermore, adenomyosis is more likely to be accompanied by a higher surgical procedure score, a prior laparotomy history and prior Cesarean section history, compared with leiomyoma [16].
Diagnostically, adenomyosis is often diagnosed with the use of MRI which can include information about leiomyoma number, size and location that can help establish the diagnosis of adenomyosis in cases that have nondiagnostic or equivocal ultrasounds [17].
Is Adenomyosis Associated with Leiomyomas?
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Adenomyosis and leiomyomas, also known as uterine fibroids, are both common conditions that can cause abnormal uterine bleeding and pelvic pain. Studies have shown that these two conditions often coexist in the same patient.
One study of 255 patients found that 85 women had both adenomyosis and leiomyomas, while 170 women had just leiomyomas [13]. Another study of 233 patients with adenomyosis found that 135 had associated uterine fibroids [18].
Specifically, women with both adenomyosis and leiomyomas had greater pelvic pain, had less fibroid burden, were more likely to be parous, and had lower body mass index compared with women with leiomyomas alone [13]. They also had higher scores of distress regarding menstrual-related pelvic pain and non-menstrual-related pelvic pain [19].
In a series of 370 women undergoing hysterectomy for abnormal uterine bleeding secondary to leiomyomas, adenomyosis was diagnosed in 170 (45.9%). There was no difference in the prevalence of adenomyosis in women with (47.1%) compared with those without (43%) at least one submucous leiomyoma [20].
In sum, adenomyosis mostly occurs in the presence of leiomyomas, and the coexistence of the two conditions may bring about special symptomatology still not fully elucidated; further research remains warranted for a better comprehension of the relationship between the two conditions and their influence on the health of women.