Three major findings deserve emphasis. First, 6 symptoms discriminated PMS as well as 17 symptoms rated in daily diaries by women who were seeking treatment for PMS. These parsimonious results clearly indicate that a small number of prospectively rated symptoms can identify the likelihood of PMS in women who seek treatment. With >90% power to detect the core symptoms, the likelihood that the excluded symptoms were false negative (type II error) results is low. Identifying a small group of symptoms that discriminate PMS among women seeking treatment also supports the concept that a clinical diagnosis for PMS might be developed around a core symptom group.
Second, the symptoms that discriminated PMS represent three domains that are widely believed to describe the syndrome and provide further evidence that PMS is a multifactorial disorder that encompasses both emotional and physical symptoms. The strongest independent predictors of PMS were mood swings and anxiety/tension, both in the emotional symptom domain and long considered predominant PMS symptoms.23–25
A recent community-based survey of premenstrual symptoms reported by women in Europe and Latin America also reported that mood swings was one of the most prevalent and severe symptoms and the leading emotional symptom experienced by these women.23
In the behavioral domain, decreased interest in activities and appetite changes/food cravings were independent predictors of PMS; aches and cramps were the independent predictors of PMS in the physical domain.
Although irritability was among the most frequently reported and severe symptoms in this study, it was not a discriminator of PMS. Irritability has long been considered a cardinal PMS symptom and is among the most responsive symptoms to selective serotonin reuptake inhibitor (SSRI) treatment for the disorder.23,24,26
Nearly all women reported irritability, however, and it was also highly correlated with half of the other PMS symptoms, which precluded its ability to discriminate PMS. These findings clearly show that irritability is likely to be part of the condition, but it is a common symptom that does not specifically define PMS.
The depression symptom also did not discriminate PMS in these data. We further examined depression in a 7-symptom model, but its addition did not alter the results of the 6-symptom model and did not add to the prediction of PMS. This suggests that depressed mood does not have a primary role in pure PMS. Depressive symptoms are among the core symptoms of PMDD as listed in the DSM-IV, although whether depressed mood is a core component of PMDD is also not clearly demonstrated.
Although the present study was not designed to compare PMS and PMDD, observations indicated a large overlap in the daily symptom ratings: 47% (255 of 541) of the PMS group also met criteria for PMDD as defined in a single menstrual cycle. As expected, the total symptom scores were higher in the PMDD group (more symptoms were required). Mood swings and decreased interest were even more predominant in the PMDD group, whereas aches were slightly higher in the PMS group. Other studies are needed to determine if there are differences in the primary symptoms of PMS and PMDD.
Third, nearly all participants reported some level of impairment in at least one domain when they sought treatment, and impairment ratings were strongly associated with the DSR scores. A previous study that evaluated criteria to identify PMS indicated that the respondents experienced reduced work productivity and quality of life regardless of the severity criteria of PMS.5
The present findings demonstrate the increase in impairment with increasing symptom severity and add further support to the evidence that PMS is strongly associated with diminished functioning in relationships and the normal activities of daily life.5,27
The sensitivity analysis showed that use of 6 symptoms classified the PMS cases nearly identically to use of 17 symptoms and further supported the hypothesis that a small number of symptoms rated daily can discriminate PMS as well as a longer symptom list. The classification results provide a balance between specificity and sensitivity and allow the clinician or researcher to select more or less restrictive cutoff points that best meet the intended objectives in their use. The classifications in the present study appear to be strong, although we know of no other studies that have identified the specificity and sensitivity of symptom scores to discriminate either PMS or PMDD. Whether correct classifications can be increased to an even higher level than the 84%–86% achieved in this study remains an important question.
Several other limitations can be considered. There is no demonstrated gold standard definition of PMS. The criteria that were used to define PMS in this study have previously demonstrated reliability and validity, but the use of other criteria might yield different results.5
The data represent generally healthy women who seek medical treatment for premenstrual symptoms and may not encompass the entire heterogeneous PMS population, particularly women with other physical or psychiatric disorders that commonly have premenstrual exacerbations. The study identified a parsimonious number of symptoms that discriminate between PMS and not PMS that can be used to evaluate women who believe they have the disorder. However, the study was not designed to provide a validated daily diary or a diagnosis of PMS, and further studies that address these objectives are needed. It is also remains for other studies to identify the associations of the identified core symptoms with treatment response, which is the essential measure of their clinical utility.
The strengths of the study include prospective DSRs that were completed before any treatment interventions, appropriate statistical power, and rigorous analysis that demonstrated notable consistency in the findings and evidence that the results are not idiosyncratic to the study sample. The findings indicate that 6 symptoms can discriminate PMS as well as 17 symptoms when prospectively rated in daily diaries to confirm PMS. The findings suggest that the burden of daily diaries could be reduced by using a smaller number of symptoms and also suggest that a clinical diagnosis for PMS might be developed around a core symptom group. Further studies are needed to construct and validate a brief daily diary and to develop the criteria for a widely accepted diagnosis of PMS.