Myometritis: inflammation of the muscular layer of the uterus

Myometritis is an inflammation of the muscular layer of the uterus (myometrium). It most often occurs not in isolation, but as part of an infectious process in the upper female reproductive system: postpartum/postabortion endometritis-myometritis, pelvic inflammatory disease (PID), or the accumulation of pus in the uterine cavity (pyometra). Clinically, myometritis presents with lower abdominal pain, fever, tenderness of the enlarged uterus, and often abnormal discharge. This condition requires prompt diagnosis and initiation of empirical broad-spectrum antibacterial therapy. [1]

In obstetrics, myometritis is almost always associated with postpartum endometritis (sometimes the term "endomyometritis" is used). According to guidelines, the first line of treatment is intravenous antibiotics that cover both aerobic and anaerobic flora, continued until clinical improvement occurs. If there is no response, a change in regimen and investigation for complications (uterine retention, pelvic abscess, pyometra) are considered. [2]

Outside of pregnancy, myometritis occurs as part of the spectrum of PID—an ascending infection involving the endometrium, fallopian tubes, ovaries, and peritoneum. PID recommendations apply: immediate empirical treatment with combination regimens against gonococci, chlamydia, anaerobes, and non-specific flora, with transition to an oral regimen after stabilization. [3]

In cases of pyometra (accumulation of pus, more common in elderly/postmenopausal patients), drug therapy is combined with drainage of the contents (dilation of the cervical canal, aspiration under ultrasound guidance). Failure to perform drainage is a common reason for the ineffectiveness of antibiotics alone. [4]

Epidemiology

Accurate population figures for "pure" myometritis are rare due to its frequent association with endometritis. Postpartum uterine infection (primarily endomyometritis) complicates up to ~3% of vaginal deliveries and up to 27% of cesarean sections; it accounts for a significant proportion of postpartum hospitalizations and the use of antibacterial therapy. [5]

In non-obstetric practice, myometritis is most often included in the structure of PID. PID has a high burden in the reproductive age; the leading etiologic agents are Chlamydia trachomatis, Neisseria gonorrhoeae and mixed polymicrobial flora, with a significant contribution of Mycoplasma genitalium, especially in "non-gonococcal-non-chlamydial" cases. [6]

The proportion of PID associated with C. trachomatis, according to models and RCT estimates, reaches ~20-35% (depending on age and country), which emphasizes the role of screening and early treatment of cervicitis in the prevention of ascending uterine infections. [7]

Pyometra occurs predominantly in postmenopausal patients (underlying factors include cervical stenosis, atrophy, tumors, and radiation therapy). Despite its relative rarity, pyometra is a source of severe infections and sepsis if drainage and antibiotics are delayed. [8]

Reasons

The main scenarios are: 1) postpartum/postoperative infection (often after cesarean section), 2) postabortion and post-manipulation infections (including septic abortion and invasive intrauterine procedures), 3) ascending infection within PID, 4) obstructive conditions with retention of contents (pyometra). [9]

The etiologic spectrum is polymicrobial: aerobes (group B streptococci, enterococci, gram-negative), anaerobes (Bacteroides spp., Peptostreptococcus), as well as C. trachomatis, N. gonorrhoeae and M. genitalium. In postpartum patients, the importance of enterococci and resistant flora increases. [10]

Factors that impede outflow and promote retention/infection (cervical stenosis, adhesions, tissue remnants/foreign bodies) maintain inflammation and require elimination of the cause (drainage, cavity revision). [11]

Rare causes are specific infections (tuberculosis, actinomycosis), more often with immunosuppression, prolonged wearing of an IUD, or in endemic regions; they require targeted diagnostics and therapy. [12]

Table 1. The main clinical situations leading to myometritis

Scenario	Examples	Key to diagnosis/treatment
Postpartum	After cesarean section, a long anhydrous period	Broad spectrum IV antibiotics until afebrile within 24-48 h. [13]
Post-abortion/post-manipulation	Septic abortion, hysteroscopy	Urgent antibiotics + evacuation of contents. [14]
PID (ascending infection)	Gonorrhea/chlamydia/mixed flora	CDC regimens: cephalosporin + doxycycline ± metronidazole. [15]
Pyometra/obstruction	Cervical stenosis, tumor, atrophy	Drainage + antibiotics. [16]

Risk factors

In obstetrics: cesarean section, prolonged anhydrous period, multiple vaginal examinations, chorioamnionitis, bacterial vaginosis, manual removal of the placenta. These factors increase the risk of postpartum endometritis and subsequent sepsis. [17]

In gynecology: STIs, “incomplete” or untimely screening/treatment of cervicitis, intrauterine interventions, long-term wearing of a copper IUD in the presence of cervicitis, obstructive conditions (cervical stenosis, adhesions). [18]

Older age and postmenopause are associated with pyometra (atrophy + stenosis), especially in the presence of concomitant cervical/endometrium tumors or after radiotherapy. [19]

Immunosuppression and specific infections (tuberculosis) increase the likelihood of atypical course and resistance to standard regimens. [20]

Pathogenesis

Ascending infection from the cervical canal leads to endometritis; in severe cases, microorganisms and inflammatory mediators spread to the myometrium (endomyometritis/myometritis). Inflammation of the myometrium impairs contractility, increases pain, and increases the risk of purulent complications. [21]

In the postpartum process, barrier function is impaired after placental separation, microbial inoculation during childbirth/surgery, and changes in local immunity play a role. Polymicrobial communities (including anaerobes) explain the need for combination therapy. [22]

In PID, uterine involvement is associated with salpingitis, parametritis, and peritonitis. Even "microbiologically unidentified" cases of PID have been shown to have serious reproductive consequences (chronic pain, infertility, ectopic pregnancy), justifying early empirical treatment. [23]

In pyometra, cervical obstruction blocks the outflow, resulting in congestion and purulent contents; without drainage, antibacterial therapy is ineffective, and the risk of perforation and peritonitis increases. [24]

Symptoms

Fever, chills, increasing pain/distension in the lower abdomen, and tenderness upon palpation of the enlarged uterus are typically noted. Abnormal discharge (purulent, foul-smelling) or, conversely, scanty discharge due to obstruction are often present. [25]

In the postpartum period, the following are alarming: fever, uterine tenderness, subinvolution, tachycardia, and profuse or foul-smelling lochia. Symptoms often develop 2-10 days after delivery/cesarean section. [26]

With PID, intermenstrual/postcoital spotting, dyspareunia, cervical tenderness, and pain with cervical movement ("cervical motion tenderness") are possible. STI testing is standard. [27]

In postmenopausal patients with pyometra, there is pain, fever, and odorous discharge; with dense cervical stenosis, there may be a “dry” clinical picture with severe pain due to overflow. [28]

Table 2. Red flags for suspected myometritis

Sign	What to suspect	Actions
Fever + painful enlarged uterus	Endometritis	Immediate broad-spectrum IV antibiotics.[29]
Severe pain/peritoneal symptoms	Pelvic abscess, perforation	Urgent visualization/consultation.
Postmenopause + foul-smelling discharge/pain	Pyometra/obstruction	Drainage + antibiotics. [30]
Recent invasive procedures	Postoperative infection	Antibiotics + RPOC/foreign body assessment. [31]

Forms and stages

Clinically, the following are distinguished: 1) acute postpartum/postabortion endomyometritis, 2) myometritis in the structure of PID (including cases requiring hospitalization), 3) myometritis with pyometra/obstruction, 4) a specific (tuberculous) variant. Each form has its own emphasis in treatment (broad spectrum, drainage, anti-tuberculosis therapy, etc.). [32]

By severity: uncomplicated (no signs of organ dysfunction) and complicated (severe course, abscess, sepsis, suspected perforation). The second option requires extensive diagnostics, possible change of antibiotics, and the participation of a surgeon/interventional radiologist. [33]

In postpartum patients, it is customary to focus on the dynamics of fever and pain in response to therapy in the first 24-48 hours; persistent fever is a signal to change the regimen and search for the lesion/pyometra/thrombophlebitis. [34]

Outside of pregnancy, criteria for hospitalization for PID (and uterine involvement) include severe pain, fever, inability to exclude surgical pathology, pregnancy, failure of outpatient therapy, etc. [35]

Complications and consequences

Without treatment, the acute process can progress to abscess formation (including tubo-ovarian abscesses), peritonitis, and sepsis. Long-term consequences have been proven in the PID scenario: infertility, chronic pelvic pain, and ectopic pregnancy. [36]

Postpartum infections are one of the causes of maternal morbidity; timely empirical therapy with IV antibiotics (clindamycin + gentamicin ± ampicillin, or beta-lactam/inhibitor) gives >85% clinical success in the early stages. [37]

Pyometra without drainage can lead to uterine perforation and generalization of infection; combined tactics (drainage + antibiotics) significantly reduce the risk. [38]

Specific infections (TB) with late diagnosis cause chronic inflammation and adhesions; etiotropic therapy is necessary according to national protocols. [39]

Table 3. Common complications and how to prevent them

Complication	Prevention
Tubo-ovarian abscess/peritonitis	Early combination therapy, assessment for abscess/pyometra. [40]
Sepsis/shock	Maternal sepsis protocols, antibiotic escalation. [41]
Infertility/chronic pain (PID)	Timely treatment of PIDs and STIs, follow-up. [42]
Perforation with pyometra	Mandatory drainage + antibiotics. [43]

Diagnostics

Basic minimum: clinical examination (fever, uterine tenderness), complete blood count (leukocytosis/C-reactive protein), cultures/PCR for STIs as indicated, pregnancy test in women of reproductive age. In the postpartum period - assessment of lochia and signs of subinvolution. [44]

Transvaginal ultrasound helps rule out uterine remnants, pyometra, and abscesses; in cases of doubt or severe cases, CT/MRI is used to detect complications and plan drainage. Radiological signs of myometritis include wall thickening and/or "heterogeneity" of the myometrium during inflammation. [45]

Blood cultures and endocervical swabs are taken before starting antibiotics, but therapy is not delayed. If enterococci/resistant strains are suspected, local resistance data are taken into account and a coating (e.g., ampicillin/sulbactam) is added. [46]

In postmenopausal patients with pyometra, evaluation for an obstructive cause (cervical/endometrium stenosis/tumor) and oncovigilance are mandatory. Diagnostic hysteroscopy/biopsy is indicated after the acute infection has subsided. [47]

Table 4. Diagnostic algorithm (briefly)

Step	What to do	For what
1	Clinic + pregnancy test	Routing (PID/postpartum/post-abortion).
2	CBC, CRP, cultures/PCR	Confirmation of inflammation, etiology.
3	TV-ultrasound (± CT/MRI)	Exclude RPOC, pyometra, abscess. [48]
4	Start antibiotics immediately	Reducing the risk of complications. [49]
5	Rate the answer 24-48 hours	Change the scheme/drainage if ineffective. [50]

Differential diagnosis

In the postpartum period, it is differentiated from endometritis without myometrial involvement (milder), pelvic vein thrombophlebitis, urinary tract infection, surgical complications (hematoma after CS), and residual tissue (RPOC). The "ultrasound + laboratory + response to therapy" combination helps differentiate diagnoses. [51]

Outside of pregnancy - from acute surgical "bellies" (appendicitis, diverticulitis), from complicated ovarian cysts, from endometriosis with painful crises; in PID, pregnancy/ectopic pregnancy is always excluded. [52]

In pyometra, differentiation is made between hematometra and serosometra; here the deciding factor is the visualization and nature of the contents during aspiration/dilation. [53]

Specific forms (tuberculosis) are differentiated by history, histology and microbiology; standard PID/postpartum infection regimens are ineffective in these cases. [54]

Table 5. What to look for in differential search

Situation	Tips	The next step
Puerperal fever	Painful uterus, lochia	Ultrasound for RPOC/pyometra; Clinda+Gent ± Ampi. [55]
"Acute abdomen", unclear etiology	Leukocytosis, pain	Rule out PID/appendicitis/abscess (CT/ultrasound). [56]
Postmenopause with pain/discharge	Vaginal atrophy, cervical stenosis	Drainage of pyometra + antibiotics. [57]
Long-term subfebrile temperature	TB exposure	Screening for TB endometritis/myometritis. [58]

Treatment

1) Postpartum endomyometritis/myometritis. First line: intravenous clindamycin + gentamicin; if enterococci/GBS are suspected or there is no response, add ampicillin or use ampicillin/sulbactam; continue until afebrile for 24-48 hours with clinical improvement. If fever persists for >48 hours during therapy, reconsider the diagnosis, perform imaging, and consider escalation (e.g., piperacillin/tazobactam) and/or drainage. [59]

2) PID with uterine involvement. Hospitalization regimens according to CDC: ceftriaxone 1 g/day IV + doxycycline 100 mg twice a day PO/IV + metronidazole 500 mg twice a day PO/IV; alternatives: cefotetan/cefoxitin + doxycycline or ampicillin/sulbactam + doxycycline (if anaerobes/enterococci are suspected). After improvement, switch to an oral course for a total of 14 days. [60]

3) Pyometra/obstructive form. Drainage (dilation of the cervical canal, aspiration) and antibiotics are mandatory. Antibiotics alone without restoring outflow are ineffective; relapses require a search for the cause of obstruction (polyp/tumor/stenosis). [61]

4) Specific infections. Tuberculous myometritis – anti-tuberculosis therapy according to national protocols; standard “gynecological” regimens do not treat the underlying cause. If suspected – histology/PCR, consultation with a phthisiatrician. [62]

Correction of associated factors. Removal of foreign bodies/residues, treatment of cervicitis/STIs in the partner, pain relief, rehydration, and thrombosis prevention in hospitalized patients. Monitoring: temperature, pulse, pain, leukocytes/CRP, ultrasound dynamics in severe cases. [63]

Table 6. Summary of treatment regimens by clinical scenarios

Scenario	Recommended starting scheme	Alternative/escalation
Postpartum endomyometritis/myometritis	Clindamycin + gentamicin IV; add ampicillin if enterococci are suspected	Ampicillin/sulbactam IV; if ineffective - piperacillin/tazobactam ± drainage
PID with uterine involvement	Ceftriaxone + doxycycline + metronidazole	Cefotetan/cefoxitin + doxycycline or ampicillin/sulbactam + doxycycline
Pyometra	Drainage + broad antibiotics	Repeat drainage; search for and correction of the cause of obstruction
Specific forms (TB)	Anti-tuberculosis therapy	Based on sensitivity results

Table 7. When to hospitalize for PID/myometritis

Criterion	Note
Severe course, sepsis, pregnancy	Immediate hospitalization and IV therapy
Suspected abscess/pyometra/peritonitis	Visualization and drainage/surgeon
Inability to exclude surgical pathology	Consultation, CT/ultrasound
Ineffectiveness of outpatient therapy 24-48 hours	Changing the scheme, expanding the spectrum

Prevention

Primary prevention includes STI prevention (barrier methods, screening and treatment for chlamydia/gonococci in risk groups), asepsis during intrauterine procedures, and adequate antibiotic prophylaxis in obstetrics/gynecology when indicated. Screening and early treatment of cervicitis reduces the risk of PID and ascending uterine infections. [64]

Secondary prevention of relapses - education on the symptoms of "early treatment", monitoring and treatment of sexual partners for STIs, assessment of the need for removal/replacement of foreign bodies, treatment of obstructive causes (stenosis, adhesions, polyps), as well as planned follow-up after discharge (after 48-72 hours and upon completion of the course). [65]

Forecast

With timely initiation of adequate antibacterial therapy and elimination of provoking factors, the prognosis is favorable: fever and pain regress within 24-48 hours, and the risk of complications is low. In most postpartum cases, clinical response is achieved in >85% of patients using standard regimens. [66]

Delayed therapy, unrecognized pyometra/abscess, and persistent pathogens worsen outcomes and increase the risk of sepsis or surgical interventions. In the PID scenario, the prognosis is influenced by the timing of treatment initiation and the completeness of the regimen: early combination therapy reduces the risk of infertility and chronic pain. [67]

FAQ

• Is myometritis the same as endometritis?

Not quite. Endometritis is an inflammation of the mucous membrane (endometrium), myometritis is an inflammation of the muscular layer; in practice, the combination ("endomyometritis") is more common, especially after childbirth/surgery or with PID. [68]

• What antibiotics are considered the "gold standard" after childbirth?

Most commonly, intravenous clindamycin and gentamicin are used; if enterococci are suspected, ampicillin is added or ampicillin/sulbactam is used. Treatment is continued until afebrile symptoms resolve within 24-48 hours and clinical improvement occurs. [69]

• Do you always need to go to hospital?

Severe cases, pregnancy, abscess/pyometra, and the inability to rule out surgical pathology are indications for hospitalization. For mild/moderate PID, outpatient treatment under supervision is possible. [70]

• Why is one antibiotic so ineffective against pyometra?

Due to outflow blockage (cervical stenosis/septum), the pus does not drain, and the lesion remains. Antibiotics must be combined with drainage. [71]

• What are the dangers of delaying treatment for PID/myometritis?

Risk of abscesses, peritonitis, sepsis, and, in the long term, infertility, chronic pain, and ectopic pregnancy. Early combination therapy reduces these risks. [72]