Acute Mastitis

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Continuing Education Activity

Mastitis can be broken down into lactational and non-lactational causes. While non-lactational causes of mastitis are less common, lactational mastitis is a common condition that affects breastfeeding women. This activity reviews the evaluation, diagnosis, and treatment of the various forms of mastitis, and highlights the role of the interprofessional team in evaluating and treating patients with these conditions.


  • Explain the pathophysiology of lactational mastitis.
  • Identify the risk factors for developing lactational mastitis.
  • Describe the presentation of a patient with idiopathic granulomatous mastitis.
  • Outline the importance of collaboration and communication amongst the interprofessional team to improve outcomes for patients affected by lactational mastitis.


Mastitis is inflammation of the breast tissue and can be broken down into lactational and non-lactational mastitis. Lactational mastitis is the most common form of mastitis. Two types of non-lactational mastitis include periductal mastitis, and idiopathic granulomatous mastitis (IGM).

Lactational mastitis, also known as puerperal mastitis, is typically due to prolonged engorgement of milk ducts, with infectious components from the entry of bacteria through skin breaks. Patients can develop a focal area of erythema, pain, and swelling, and can have associated systemic symptoms, including fever. This occurs most commonly in the first six weeks of breastfeeding but can occur at any time during lactation, with most cases falling off after 3 months.[1]

Periductal mastitis is a benign inflammatory condition affecting the subareolar ducts and occurs most commonly in reproductive-aged women. Idiopathic granulomatous mastitis is a rare and benign inflammatory condition that can clinically mimic breast cancer.[1] The condition occurs primarily in parous women, most commonly within 5 years of giving birth.[1]


Lactational mastitis is most commonly caused by bacteria that colonize the skin, with Staphylococcus aureus being the most common. Methicillin-resistant S. aureus (MRSA) has become an increasingly common cause of mastitis, and risk factors for MRSA should be considered. Other causative organisms include Streptococcus pyogenes, Escherichia coli, Bacteroides species, and Coagulase-negative staphylococci. Risk factors for lactational mastitis include prior history of mastitis, nipple cracks and fissures, inadequate milk drainage, maternal stress, lack of sleep, tight-fitting bras, and use of antifungal nipple creams.[2][3]

The cause of periductal mastitis is not clear. However, many suggest that smoking may be associated with the development of the condition through direct damage to the ducts and subsequent inflammation. Bacteria are isolated in cultures in 62%-85% of patients with periductal mastitis, and the most common causative organisms include Staphylococcus aureus, Pseudomonas aeruginosa, Enterococcus, Bacteroides, and Proteus species.[4] Obesity and diabetes mellitus have also been implicated as possible risk factors.[5]

The etiology of idiopathic granulomatous mastitis (IGM) remains unclear. Autoimmune disease, trauma, lactation, oral contraceptive pill use, and hyperprolactinemia have all been implicated as possible causes.[6] There may also be an association with Corynebacterium, especially in patients with the histological findings of cystic neutrophilic granulomatous mastitis (CNGM).[7]


Worldwide, lactational mastitis occurs in 2%-30% of breastfeeding women.[8] In the United States, the reported incidence is between 7% to 10%.[2][9] The incidence is the highest in the first three weeks postpartum.[10]

Patients with periductal mastitis are most often reproductive-aged females, and it is almost exclusively associated with tobacco use.[10] Periductal mastitis occurs in 5% to 9% of women worldwide.[11]

IGM is very rare, and its true prevalence is unknown.[12] IGM occurs in parous women, usually within five years of giving birth. The majority of patients affected report a history of breastfeeding and develop symptoms six months to two years after the cessation of breastfeeding.[13] The mean age of onset is 32 to 34 years old.[13] Several studies have shown a higher incidence of IGM in Hispanic populations.[14][15][16][12]


Lactational mastitis occurs due to a combination of inadequate drainage of milk, and the introduction of bacteria. Common scenarios leading to poor milk drainage include infrequent feeding, an oversupply of milk, rapid weaning, illness in mother or child, and a clogged duct.[3] The inadequately drained milk stagnates, and organisms grow, leading to infection. It is thought that bacteria (usually from the infant’s mouth, or mother’s skin) gain entry to the milk via cracks in the nipple.[2]

The pathophysiology of periductal mastitis remains unclear. Smoking is thought to play a role in the pathogenesis, by either directly or indirectly damaging the ducts leading to subsequent necrosis and infection.[17] Squamous metaplasia is a finding in patients with this condition, and it is thought that desquamated metaplastic cells may form a plug leading to blockage of the duct and subsequent infection.[18] One recent study showed there to be an upregulation of IFN- γ, and IL-12A in patients with periductal mastitis compared to the control.[5] These are cytokines secreted by TH1 cells, and play a role in the eradication of foreign pathogens. The upregulation of these cytokines suggests that immune responses may play a role in the pathogenesis of periductal mastitis. 

The pathophysiology of IGM remains unclear, but the most widely accepted theory points to autoimmune destruction initiated by a specific trigger, such as trauma, bacteria, or extravasated milk.[14] This causes leakage of secretions from the ducts into the breast tissue, and inflammatory cells infiltrate and cause a granulomatous response.[19]


Idiopathic granulomatous mastitis (IGM) is characterized by non-caseating granulomas with epithelioid histiocytes and multinucleated giant cells in the breast lobules. In the CNGM subtype, the classic histologic features are non-caseating granulomas with characteristic cystic spaces lined by neutrophils containing gram-positive cocci.[20][21] It is important to note that a biopsy is not routinely recommended for the evaluation of periductal mastitis or lactational mastitis.

History and Physical

Lactational mastitis is often preceded by either engorgement or a focally blocked duct. Patients may give a history of these associated symptoms before the development of the classic features of mastitis. Lactational mastitis is characterized by a focal, firm, erythematous, swollen, and painful area of one breast, plus a fever (higher than or equal to 100.4 degrees Fahrenheit). Patients often experience systemic symptoms such as chills, myalgias, and malaise.

Features of periductal mastitis include a periareolar or subareolar mass, that may be associated with pain and erythema. Patients may present with nipple inversion, thick nipple discharge, breast abscess, or draining fistulas.[22]

IGM most often presents with a firm, unilateral breast mass. Other findings can include nipple retraction, skin thickening, axillary adenopathy, ulceration, and abscess formation.[23] Many of these features overlap with the presenting features of breast malignancy, and this can sometimes be misdiagnosed early on. Patients with IGM can also experience extramammary manifestations, including arthralgias, episcleritis, and skin changes.[24]


The diagnosis of lactational mastitis is based on history and clinical findings. If there is concern that the patient may have a breast abscess, a breast ultrasound can be obtained. If an abscess is present, hypoechoic areas of purulent material will be seen. For patients with a severe infection that is unresponsive to initial antibiotic therapy, a culture of breast milk can be useful to guide appropriate antibiotic selection. However, this is not routinely needed. Similarly, if there is a concern for bacteremia in a patient with severe mastitis, blood cultures should be obtained. However, these are not a part of the routine workup.[11] 

Periductal mastitis is primarily a clinical diagnosis. If nipple drainage is present, gram stain and culture should be sent to identify any associated organisms. If there is an associated mass and concern for malignancy, ultrasound or mammography should be obtained.[11]

Because the clinical features of IGM overlap with those of breast cancer, a biopsy must be done to make this diagnosis. Core needle biopsy or excisional biopsy are both viable options. Because of the proposed association between hyperprolactinemia and IGM, a prolactin level may be sent. Ultrasound and mammography are not adequate to distinguish IGM from breast malignancy.[13]

Treatment / Management

The initial management of lactational mastitis is symptomatic treatment.[25] Continuing to fully empty the breasts has shown to decrease the duration of symptoms in patients treated both with and without antibiotics. Patients should be encouraged to continue to breastfeed, pump, or hand express.[19][8][9] If the patient stops draining the milk, further stasis occurs, and the infection will progress. Non-steroidal anti-inflammatory drugs (NSAIDs) can be used for pain control. Heat applied to the breast just before emptying can help increase milk letdown and facilitate with emptying.[25]Cold packs applied to the breast after emptying can help reduce edema and pain.

If the symptoms of lactational mastitis persist beyond 12 to 24 hours, antibiotics should be administered.[8][9] Because S. aureus is the most common cause, antibiotic therapy should be tailored accordingly. In the setting of mild infection without MRSA risk factors, outpatient treatment can be initiated with dicloxacillin or cephalexin. If the patient has a penicillin allergy, erythromycin can be used. If the patient has risk factors for MRSA infection, treatment options include trimethoprim-sulfamethoxazole (TMP-SMX) or clindamycin. TMP-SMX should be avoided in women who are breastfeeding infants less than 1-month-old, and in infants who are jaundiced or premature. If a patient requires hospitalization, empiric treatment with vancomycin should be initiated until cultures and sensitivities return. There are not sufficient studies on the appropriate duration of outpatient treatment, but most sources recommend a 10-14 day course.[10]

Periductal mastitis is treated empirically with amoxicillin-clavulanate. Alternative options include dicloxacillin plus metronidazole or cephalexin plus metronidazole. If an abscess is present, ultrasound-guided needle aspiration plus antibiotic therapy is the preferred management strategy.[11] Periductal mastitis is often a recurring condition. If a patient has recurrent infections, surgical excision of the inflamed ducts may be required.[26] 

The treatment of IGM remains controversial. Current treatment strategies vary broadly and can include observation, corticosteroids, immunosuppressants, antibiotics, and surgery.[23] IGM is a benign condition that typically resolves without treatment in an average of 5 months.[23] A recent study showed the time to resolution of symptoms did not differ in patients who were managed with medications and with those managed with observation and supportive care.[23] Surgical excision is an option, but there is a reported 10% recurrence, even with surgical treatment. If IGM is complicated by secondary infection, antibiotics should be chosen based on culture and sensitivities.

Differential Diagnosis

The differential diagnosis of the three forms of mastitis differs significantly. The common differential diagnoses for each are as follows:

Lactational mastitis

  • Breast engorgement
  • Clogged duct
  • Breast abscess
  • Galactocele
  • Inflammatory breast carcinoma

Periductal mastitis

  • Duct ectasia
  • Breast abscess
  • Breast carcinoma

Idiopathic granulomatous mastitis

  • Breast carcinoma
  • Wegeners granulomatosis
  • Tuberculosis
  • Sarcoidosis
  • Breast abscess


The majority of patients with mastitis will recover with appropriate treatment. The recurrence rate for each type of mastitis varies as follows: 

  • Lactational mastitis: 8%-30% [27][28]
  • Periductal mastitis: 4%-28% [17]
  • Idiopathic granulomatous mastitis: 20%-78% [29][30]

One study reported that 38% of patients with IGM reported significant scarring, and 29% reported long term pain.[30]


One of the most common complications of lactational mastitis is early termination of breastfeeding. The disease of the breast and associated pain are some of the most commonly cited reasons for early cessation of breastfeeding.[25][31] A breast abscess is another complication of lactational mastitis and occurs in 3% to 11% of patients.[32][25] The development of a breast abscess is more common if mastitis is not treated early.

Periductal mastitis and IGM can both be complicated by abscess or fistula formation. Both forms of non-lactational mastitis are associated with recurrence and can lead to scarring and deformity of the breast tissue.

Deterrence and Patient Education

Lactational mastitis usually develops after a period of incomplete drainage and milk stasis. It is important to educate patients on ways to limit this stasis to prevent mastitis. Things to discuss may include the appropriate frequency of feeding and proper infant latching technique. Nipple pain is a common complaint in breastfeeding women and may lead to less frequent nursing. This increases milk stasis, thus increasing their risk of developing mastitis. It is important to counsel patients on ways to manage and decrease their pain. Patients with lactational mastitis may feel inclined to stop breastfeeding during their period of illness, possibly due to a combination of the discomfort and pain, as well as the concern of passing the infection to their infant. Providers should ensure the patient that breastfeeding with mastitis is safe and that they should continue to do so if desired.[33] If the patient does not wish to continue to breastfeed, they should be counseled on the importance of continuing to empty the breasts and taught alternative methods such as the use of a breast pump or manual expression. 

In addition to patient education, provider education is equally important. One small study showed that some providers are misinforming patients with mastitis that they must stop breastfeeding while infected.[28] Not only does this increase the likelihood of the patient developing an abscess, but it also contributes to early termination of breastfeeding, which robs both the patient and the infant of the associated benefits.[33]

Periductal mastitis is found almost exclusively in smokers. Encouraging smoking cessation is important and may help reduce the risk of recurrent inflammation.

Pearls and Other Issues

Take-home points

  • One of the most important considerations in the treatment of lactational mastitis is the need to continue to empty the breasts – encourage patients to continue to breastfeed if desired, and if not, encourage the use of a breast pump or hand expression.
  • Lactational mastitis can be managed conservatively with supportive measures for the first 12 to 24 hours. If symptoms do not improve after this period, antibiotics should be started.
  • If symptoms of lactational mastitis do not improve in 24 to 28 hours, consider the possibility of a breast abscess, and obtain an ultrasound.
  • Idiopathic granulomatous mastitis is a rare condition that is often mistaken for breast carcinoma. A biopsy must be done to diagnose this condition and to rule out more serious pathology.
  • The majority of patients with mastitis can be managed as outpatients. Examples of scenarios in which a patient may require hospitalization include the following: hemodynamic instability, intolerance to oral intake, severe dehydration, and recurrent infection that has failed outpatient management.

Enhancing Healthcare Team Outcomes

Lactational mastitis is a common condition among breastfeeding women. There are several modifiable risk factors discussed in this article, such as feeding too infrequently, the use of certain nipple creams, poor latching techniques, and tight-fitting bras, that predispose women to this disease. Education soon after delivery to raise maternal awareness on these risk factors could potentially lead to decreased incidence of mastitis. An interprofessional team approach should be taken when educating these women. Input from the physician, nursing staff, and lactation consultant should be incorporated in a consolidated effort to help decrease the incidence of this disease.

While patients with lactational mastitis may seek care from their obstetrician, it is not uncommon for these patients to present to urgent care facilities, emergency departments, or family practice physicians for evaluation. For this reason, it is important for physicians in each of these settings to be aware of the appropriate management of this condition. All medical staff caring for patients with mastitis should be aware of the recommendation that these patients continue to breastfeed, and that sudden cessation of breastfeeding increases the risk of abscess formation.[Level 3][33]  

For patients seeking care in the emergency department, there are often long wait times, and during this time, pumping or nursing may be necessary. Some hospitals have pumps that are able to be checked out to patients while in the emergency department. Emergency physicians should be aware of their hospital policy to obtain a pump if one is needed. This can often be coordinated with either the lactation consulting team or the obstetrics team.

If a physician is unsure whether or not an antibiotic they are prescribing is safe to take while breastfeeding, they may recruit the expertise of a pharmacist to ensure that the patient is getting a medication that will allow her to continue to breastfeed her child.

Article Details

Article Author

Melodie M. Blackmon

Article Author

Hao Nguyen

Article Editor:

Pinaki Mukherji


7/18/2022 11:39:44 PM



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