The Annex: 90 women, two months of diaries, three patterns of PMDD, and a control group that is 40 or 44 depending on where you read

The Annex reads the method behind the headline. Today’s: Uppsala University says premenstrual dysphoric disorder (PMDD), the severe form of premenstrual syndrome, “does not follow any universal pattern” but falls into three subtypes¹. The paper, led by Ella Schleimann-Jensen and Erika Comasco, appeared in Nature Communications on Tuesday².

The design. Women with PMDD and healthy controls rated their symptoms every day for two menstrual cycles on an online version of a standard scale, the Daily Record of Severity of Problems, with 21 items each scored from 1 (“not at all”) to 6 (“extreme”)². The diagnosis was prospective: symptoms had to rise by more than 50% from the follicular to the luteal phase². Participants came from the screening phase of two Uppsala drug trials, one of escitalopram and one of a progesterone-receptor modulator, recruited through newspaper, campus and social media adverts².

The result. Statistical modelling of the diaries found three groups: severe PMDD with early onset, about two weeks before menstruation and peaking about five days before; severe PMDD with late onset, rising about ten days before and peaking around the start of menstruation; and a moderate late-onset group peaking about four days before¹. Over time, rising anxiety tended to be followed by more irritability, low mood and mood swings¹. The paper calls anxiety “a central symptom” in how the episode unfolds².

The footnotes that matter. The press release says 90 women with PMDD and 40 controls¹; the paper reports 44 controls and 134 participants in total². Small, but it is the kind of thing a reader should check. The authors write that “no separate sample size calculation was performed” for this observational analysis and that it “was not separately preregistered”². The dynamic model was limited to four core symptoms because adding more would risk “unreliable estimates given the sample size”². And the strict 50% threshold, they note, “may limit generalizability to less severe PMDD presentations”².

What the authors themselves say. Comasco is plain that the study “cannot explain why these differences occur”, and that more research is needed before the patterns can predict one person’s course¹.

For you. If you, or someone you live with, recognise this, the most useful tool in the paper is the cheapest: a daily diary over two cycles. It is how the diagnosis was made here, and it gives a doctor something better than memory to work with.