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most cases occur during lactation and are caused by staphylococcus aureus and streptococcus species ; parasites and mycobacterium tuberculosis have rarely been reported to cause breast infections .
recurrent mastitis and breast abscesses may be due to delayed , incomplete , or inappropriate therapy as well chronic staphylococcus infections .
they may also be due to underlying breast lesions . however , the disease is clinically and radiologically very difficult to diagnose .
we report a case of recurrent bilateral mastitis shown pathologically to be due to nontuberculous mycobacterial ( ntm ) infection .
a 35-year - old korean woman admitted to the in - patient clinic of our institution presented with swelling , pain , and rigidity of the left breast that began 4 days previous .
physical examination revealed a palpable tender mass , erythema , and swelling in the upper half of the left breast , extending to the nipple .
she had no previous history of trauma , operation , or family history of breast cancer ; further , she was not immunocompromised .
prior to admission , the patient had a history of recurrent breast infections beginning in july 2007 .
she was treated for mastitis of her right breast with pus formation , and she made complete recovery .
she underwent breast biopsy for a mass on her right breast , and a fluid sample was cultured . based on the culture results ,
the lesion was diagnosed as an ntm infection , and the patient was treated with combined antibiotic therapy for 12 months .
the patient underwent biopsy for this lesion as well , which was also diagnosed as an ntm infection .
we performed routine breast ultrasonography , which revealed a 2.8 cm , ill - defined , partially multilobulating contoured mass with heterogeneous internal echogenicity in the subareolar area , with diffuse edema of the left breast ( figure 1 ) .
several small lymph nodes less than 1 cm in short diameter were visible in the left axilla level i. the patient also underwent bilateral dynamic contrast - enhanced magnetic resonance imaging of the affected breast to further evaluate the extent of the lesion and the potential for hidden malignancies ( figure 2 ) .
dynamic contrast - enhanced magnetic resonance imaging revealed a 2.42.4 cm iso- to high - signal intense mass on t2 wi and iso - intense on t1 wi , which showed peripheral rim enhancement after contrast injection .
associated findings included diffuse parenchymal enhancement of the upper outer to central portion of the left breast with thickening of the overlying skin .
this lesion appeared to be an abscess associated with mastitis . to exclude the possibility of hidden malignancies , a biopsy was performed .
considering the previous histopathologic findings in 2008 , 2010 , and 2012 , granulomatous mastitis was suspected ( figure 3 ) , with no acid - fast bacilli visible on ziehl - neelsen staining .
although we could not confirm the identity by specimen culture , paraffin - embedded tissue samples were positive for ntm by polymerase chain reaction .
based on the clinical course of recurrent infections over 5 years , previous histopathologic findings , and positive polymerase chain reaction results , a clinical diagnosis of ntm infection was made .
clarithromycin ( 1,000 mg / day ) was administered in combination with ciprofloxacin ( 1,000 mg / day ) for 1 year . because the lesion progressed to pus formation
the patient underwent a follow - up breast ultrasonography after 1 month that showed lesion improvement .
she has been followed up for 1 year with no clinical or radiological evidence of recurrence .
the most common organisms found in these infections included mycobacterium fortuitum , m. avium , m. abscessus , and less commonly , m. chelonae .
ntm should be considered as a source of infection when standard bacterial culture results are negative .
. it can be difficult to differentiate noninfectious and infectious mastitis at early stages ; hence , antibiotics are used in either case . when m. tuberculosis ( tb ) is suspected , anti - tb therapy may be required .
a lack of response to anti - tb therapy or a diffusely deformed breast with draining sinuses may require surgical intervention .
once an ntm organism is isolated by culture , the infection should be treated with targeted combined antibiotic therapy .
the most commonly reported cause of skin and soft tissue disease in ntm infections is m. fortuitum .
the majority reported an association between onset of infection and breast implants or reconstructive surgery .
they recommended removal of the infected implant in addition to appropriate antimicrobial therapy for the management of implant - associated ntm infections .
for postoperative wound infections , the removal of implants or infected foreign bodies was required .
patients treated according to in vitro susceptibilities of isolated colonies have shown good results in a previous study ; these targeted therapies are considered essential for infection management and antimicrobial stewardship .
a primary panel of drugs for susceptibility testing may include amikacin , cefotoxin , ciprofloxacin , clarithromycin , doxycycline , imipenem , and a sulphonamide .
however , few studies have reported ntm breast infections not associated with implants . to our knowledge , there has been only one published report of spontaneous breast abscess due to m. fortuitum ; another report described infection following nipple piercing .
when m. tuberculosis complex species are suspected as the source of infection , targeted antibacterial therapy is recommended .
although we could not confirm the diagnosis by culture , the initial biopsy requested by the regular physician was positive for ntm .
the patient was not immunocompromised and had no history of breast surgery , including implant insertion . therefore
, the exact cause of the recurrent ntm infection could not be determined . in conclusion , although it is difficult to differentiate from other causes due to nonspecific imaging findings , ntm should be considered for breast infections that recur despite standard antibiotic therapy .
since recurrent bilateral breast infection due to nontuberculous mycobacterium ( ntm ) is rare , its diagnosis is easily overlooked ; in addition , complete recovery is often difficult to achieve . 
 we report a case of recurrent bilateral infection in a 35-year - old woman who had completed treatment for ntm . 
 although various infectious diseases show similar clinical conditions and imaging findings , recurrences should raise suspicion of ntm infection , and this possibility should be considered in differential diagnoses .