A new mother with night sweats

Case scenario

Sally is a 35-year-old woman who presents for her three-monthly contraceptive injection of depot medroxyprogesterone. She mentions in passing that since the birth of her second child, nine months previously, she has been experiencing night sweats three or four times a week. She has no obvious focus of infection, no pain and no other systemic symptoms, although she says she often feels very tired. She also reports that she is still producing some breast milk despite having stopped breastfeeding six months previously.

Sally recalls that about two years ago, before she conceived her second child, she was quite sick with an ‘ovarian infection’ and then an ectopic pregnancy.

Sally’s pelvic ultrasound results are normal, as are the results of urine and blood tests, including a full blood count, erythrocyte sedimentation rate, C-reactive protein level, thyroid function and serum prolactin level. Her serum follicle-stimulating hormone and other reproductive hormone levels are in the normal range for the luteal phase of the menstrual cycle.

What could be causing Sally’s night sweats?