Pelvic Inflammatory Disease

Introduction

Pelvic inflammatory disease (PID) is infection and inflammation of the upper female genital tract, encompassing endometritis, salpingitis, oophoritis, and, in severe cases, tubo-ovarian abscess and pelvic peritonitis. It most commonly results from ascending infection from the lower genital tract (cervix and vagina) into the uterus, fallopian tubes and ovaries.¹

PID predominantly affects sexually active women, with the highest incidence in those under 25. It is a leading preventable cause of tubal infertility and ectopic pregnancy, which is why prompt empirical treatment - even before microbiological confirmation - is central to management.

Aetiology

Chlamydia trachomatis and Neisseria gonorrhoeae are the most frequently identified causative organisms, but PID is often polymicrobial, and a substantial proportion of cases have no organism isolated despite a clear clinical picture.² Other implicated organisms include Mycoplasma genitalium, and anaerobic and aerobic bacteria normally found in the vaginal flora, which ascend alongside the primary pathogen once the normal cervical barrier is disrupted.

Non-sexually transmitted causes are less common but include instrumentation of the uterus (post-termination of pregnancy, post-partum, insertion of an intrauterine device, hysteroscopy) that disrupts the natural barrier to ascending infection.

Risk factors

• Age under 25
• New or multiple sexual partners
• Previous sexually transmitted infection or previous PID
• No barrier contraception
• Recent instrumentation of the uterus (termination of pregnancy, IUD insertion, hysteroscopy)
• Lower socioeconomic status (a marker of, rather than a direct cause of, differing STI exposure and access to care)

Clinical features

Presentation ranges from mild, non-specific symptoms to severe peritonitis, and a significant proportion of cases are subclinical, only recognised later when a woman presents with subfertility.¹

• Bilateral lower abdominal or pelvic pain: the most common symptom, typically of gradual onset
• Deep dyspareunia
• Abnormal vaginal discharge: often purulent or mucopurulent
• Abnormal bleeding: intermenstrual, postcoital, or breakthrough bleeding, reflecting cervicitis and endometritis
• Fever: present in more severe disease
• Right upper quadrant pain: suggests perihepatic involvement (Fitz-Hugh-Curtis syndrome, see below)

On examination, the classic triad is cervical excitation (pain on moving the cervix during bimanual examination), adnexal tenderness (usually bilateral, though can be unilateral), and cervicitis or mucopurulent discharge seen on speculum examination. A palpable, tender adnexal mass raises concern for a tubo-ovarian abscess.

Differential diagnosis

• Ectopic pregnancy: always perform a pregnancy test
• Appendicitis: more often unilateral, right-sided, without cervical excitation
• Ovarian cyst accident (torsion, rupture, haemorrhage): typically more acute in onset and unilateral
• Endometriosis: more chronic, cyclical pattern
• Urinary tract infection
• Irritable bowel syndrome

Investigations

PID is a clinical diagnosis, and the threshold for starting treatment should be low because the consequences of delayed treatment (tubal damage) are more serious than the consequences of unnecessary antibiotics in someone who turns out not to have PID.²

Bedside and laboratory

• Pregnancy test - to exclude ectopic pregnancy, which is an essential differential
• Endocervical and high vaginal swabs (NAAT) for chlamydia and gonorrhoea - a negative result does NOT exclude PID and should not delay or stop treatment if clinical suspicion is high
• Full blood count and CRP - raised inflammatory markers support the diagnosis but are not required to start treatment
• HIV and syphilis screening as part of a full sexual health screen, given the shared risk factors

Imaging

Pelvic ultrasound is not required to make the diagnosis but is useful if a tubo-ovarian abscess or another differential (ovarian cyst, ectopic pregnancy) is suspected. Laparoscopy is the gold-standard investigation, allowing direct visualisation of tubal inflammation and microbiological sampling, but is reserved for diagnostic uncertainty or failure to respond to treatment, not for routine use.

Management

Empirical antibiotic therapy should be started promptly on clinical suspicion, without waiting for swab results, because delayed treatment increases the risk of tubal damage and infertility.¹ Regimens are chosen to cover chlamydia, gonorrhoea and anaerobes.

Admission and IV antibiotics are indicated for a tubo-ovarian abscess, failure to respond to oral therapy, severe systemic illness, pregnancy, or where surgical intervention may be needed (e.g. drainage of an abscess). Mild-to-moderate PID can be managed as an outpatient with oral antibiotics and review.

Contact tracing and partner treatment

Referral to genitourinary medicine (GUM) for contact tracing is essential, as is treating current sexual partner(s) empirically for chlamydia and gonorrhoea, regardless of their symptoms, to prevent reinfection. Sexual intercourse should be avoided until treatment is complete and partners have been treated.

IUD/IUS in situ

Removal of an intrauterine contraceptive device is considered, particularly in moderate-to-severe disease or if there is no improvement within 48-72 hours of starting antibiotics, but is not mandatory in every case - the decision is individualised, balancing infection control against unwanted pregnancy risk if the device is removed.

Fitz-Hugh-Curtis syndrome

Fitz-Hugh-Curtis syndrome is perihepatitis - inflammation of the liver capsule and the peritoneum around it - occurring as a complication of PID, thought to result from direct spread of infection along the paracolic gutter or via lymphatic/haematogenous spread. It presents with right upper quadrant pain, sometimes pleuritic in nature, which can mimic cholecystitis. 'Violin-string' adhesions between the liver capsule and the anterior abdominal wall or diaphragm are a classic finding at laparoscopy. Management is the same antibiotic regimen as for PID itself; adhesiolysis is occasionally required for chronic pain.

Complications

• Tubal infertility: risk rises with each episode of PID (roughly 10-12% after one episode, higher with repeated episodes) due to tubal scarring and occlusion³
• Ectopic pregnancy: tubal damage increases the risk several-fold
• Chronic pelvic pain: from adhesions and chronic inflammation
• Tubo-ovarian abscess: a collection requiring IV antibiotics and, if not resolving, radiological or surgical drainage
• Fitz-Hugh-Curtis syndrome (see above)
• Recurrent PID

Red flags

Prognosis

With prompt treatment, most women recover fully without long-term sequelae. However, outcomes are strongly time-dependent: the risk of tubal infertility, ectopic pregnancy and chronic pelvic pain rises significantly with delayed treatment and with recurrent episodes, which underpins the emphasis on starting antibiotics empirically on clinical suspicion rather than waiting for confirmatory tests.