The answer is B. Pelvic inflammatory disease
Lower abdominal pain with cervical motion tenderness and adnexal tenderness in a sexually active young woman is pelvic inflammatory disease, and the diagnosis is deliberately built to be made clinically rather than confirmed. PID is ascending infection of the upper genital tract — endometritis, salpingitis, tubo-ovarian abscess, and pelvic peritonitis — usually polymicrobial, with Chlamydia trachomatis and Neisseria gonorrhoeae the classic initiating organisms alongside anaerobes, gram-negative rods, streptococci, and genital mycoplasmas. The single most important management principle is the low treatment threshold. The CDC advises empiric treatment in a sexually active young woman with pelvic or lower abdominal pain, no other identified cause, and any one of cervical motion tenderness, uterine tenderness, or adnexal tenderness. One minimum criterion is enough. The reason is a risk calculation rather than diagnostic confidence: the cost of treating a woman who turns out not to have PID is a course of antibiotics, while the cost of missing it is tubal scarring with infertility, a sixfold to tenfold increase in ectopic pregnancy, and chronic pelvic pain — and each additional episode roughly doubles the infertility risk. Additional criteria that raise specificity include oral temperature above 38.3°C, mucopurulent cervical discharge or a friable cervix, abundant white cells on saline microscopy of vaginal fluid, an elevated ESR or CRP, and documented cervical infection with gonorrhea or chlamydia. Outpatient treatment is ceftriaxone 500 mg intramuscularly once, plus doxycycline 100 mg twice daily for 14 days, plus metronidazole 500 mg twice daily for 14 days — ceftriaxone for gonorrhea, doxycycline for chlamydia, and metronidazole for the anaerobes, which current guidance includes routinely rather than optionally. Know the admission criteria: pregnancy, failure of or inability to tolerate oral therapy, severe illness with high fever or vomiting, a tubo-ovarian abscess, or a surgical emergency that cannot be excluded. Two associated points are heavily tested. Fitz-Hugh-Curtis syndrome is perihepatitis complicating PID, presenting as right upper quadrant pleuritic pain with violin-string adhesions between the liver capsule and the abdominal wall. And treat sexual partners from the preceding 60 days and counsel abstinence until both partners complete therapy, or the patient is simply reinfected. Test for HIV and syphilis, and remember that an intrauterine device does not need to be removed if the patient is responding to therapy. Sorting the distractors: a ruptured ovarian cyst produces sudden unilateral pain often at midcycle or after intercourse, without fever, purulent discharge, or cervical motion tenderness; ectopic pregnancy is the diagnosis you must exclude first in any woman of reproductive age with pelvic pain, which is why the pregnancy test comes before everything else — here it is negative, which takes it off the table; acute appendicitis migrates from the periumbilical region to a focal right lower quadrant point with rebound, guarding, and anorexia, and it does not cause bilateral adnexal tenderness or a purulent cervix; and endometriosis causes cyclic dysmenorrhea, deep dyspareunia, and infertility building over years, with a normal temperature, no discharge, and often uterosacral nodularity on examination rather than an acute febrile illness.
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