Address for correspondence: Daniel W. Cramer, Department of Obstetrics, Gynecology, and Reproductive Biology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115. Voice: 617-732-4895; fax: 617-732-4899.
dcramer{at}partners.org
Advances in understanding the epidemiology of endometriosis
have lagged behind other diseases because of methodologic problems
related to disease definition and control selection. Nevertheless,
a better picture of the epidemiology of endometriosis has emerged
over the past few decades. Prevalence estimates of the disease
in clinic populations vary from about a 4% occurrence of largely
asymptomatic endometriosis found in women undergoing tubal ligation
to 50% of teenagers with intractable dysmenorrhea. General population
incidence during the 1970s in this country has been suggested
to be 1.6 per 1000 white females aged 15-49, while a more current
study based upon hospital discharges finds endometriosis as
a first listed diagnosis in 1.3 per 1000 discharges in women
aged 15-44. There is a clinical impression that blacks have
lower rates of endometriosis and Orientals have higher rates
than whites. A variety of personal risk factors for endometriosis
have also been described. Women with endometriosis may be taller
and thinner. Menstrual factors reported to increase risk include
dysmenorrhea, early menarche, and shorter cycle lengths. There
is support for the idea that lifestyle exposures that might
raise or lower estrogen levels could affect risk, including
a decreased risk associated with smoking and exercise and an
increased risk associated with caffeine or alcohol use. These
risk factors appear to be compatible with the central importance
of retrograde menstruation influenced by outflow obstruction
that might affect its amount, immune factors that might affect
its ability to be cleared, or hormonal stimuli that might affect
its growth. In this model, dysmenorrhea could be either a disease
symptom or a manifestation of outflow obstruction. Nulliparity
could be either a consequence of disease or a cause since nulliparous
women would not have the benefit of cervical dilation associated
with labor and delivery. Since there is evidence that family
history is a risk factor for disease, a challenge is how to
integrate genetic factors into the model. The genetics of endometriosis
might be advanced if we could identify an "endometriosis phenotype".
We propose that this may consist of early menarche, short cycles,
painful periods, subfertility, and possibly tall stature that
could be explained by genetic factors that predispose to poor
endowment of germ cells and canalization defects of the cervix.
The value of establishing an "endometriosis phenotype" is that,
as candidates for genetic markers are identified, particular
genotypes can be correlated with these factors even if a formal
diagnosis of endometriosis has not been made. Additional well-designed
case-control and cohort studies will be necessary to test theories
related to pathogenesis, establish the precise relationship
between reproductive morbidity and endometriosis, identify specific
genetic factors, and establish long-term risks.
