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Community-Acquired Methicillin-Resistant Staphylococcus aureus USA 300 Genotype Causing Pyomyositis and Kikuchi-Fujimoto Disease

Fahmy, Samer MD; Yacoub, Michael MD; Saravolatz, Louis D. MD

Infectious Diseases in Clinical Practice: September 2008 - Volume 16 - Issue 5 - p 321-323
doi: 10.1097/IPC.0b013e318162a9b8
Case Reports

Pyomyositis is a rare infection of skeletal muscle originally described in tropical regions, but recently, occurrences in temperate climates have become more frequent. We describe a 39-year-old previously healthy man living in a temperate region that presented with a rapidly enlarging left breast mass. He had been experiencing low-grade fevers with mild tenderness and weight loss over a 2-week period. Computed tomography of the chest revealed multiple bilateral septic pulmonary emboli with an infiltrative process involving the entire left pectoralis major muscle. Sarcoma was suspected, and thus, biopsy was necessary. Open biopsy of the mass resulted in drainage of a large amount of purulent discharge. Community-acquired methicillin-resistant Staphylococcus aureus was cultured and confirmed with pulse-field gel electrophoresis showing staphylococcal chromosomal cassette mec type IV and Panton-Valentine Leukocidin (+). The patient was discharged on intravenous vancomycin after resolution of fevers. He returned to the emergency department 2 weeks later with recurrence of fevers, chills, and flulike symptoms. He had generalized lymphadenopathy particularly in the anterior cervical and inguinal lymph node chains. The hemoglobin, platelet, and white blood cell count, which were previously normal, were significantly reduced. Repeat computed tomographic scan showed splenomegaly with generalized lymphadenopathy and resolution of the chest wall mass and septic emboli. A lymph node biopsy confirmed a diagnosis of Kikuchi-Fujimoto disease, a self-limiting hyperimmune response to infection. Human immunodeficiency virus, cytomegalovirus, and toxoplasmosis testing was negative. Resolution of the pancytopenia occurred with spontaneous improvement of lymph nodes; thus, a causal association was assumed.

Department of Internal Medicine, St John Hospital and Medical Center, Warren; and Wayne State University School of Medicine, Detroit, MI.

Address correspondence and reprint requests to Samer Fahmy, MD, 3137 Waterside Cir., Boynton Beach, FL 33435. E-mail:

Community-acquired methicillin-resistant Staphylococcus Aureus (CA-MRSA) has become an endemic problem in many areas of the United States. Clinical manifestations have involved predominantly skin and soft tissue infections.1-4

Pyomyositis is a rare infection of skeletal muscle. Although originally described in tropical regions, occurrences in temperate climates have become more frequent. Staphylococcus aureus is the most common pathogen implicated in pyomyositis. In addition, CA-MRSA has been described recently as a cause of pyomyositis.1

Kikuchi-Fujimoto disease (KFD) is a poorly understood entity that usually occurs in response to infection or malignancy. It is thought to be a hyperimmune response to an acute insult, usually infectious. To the best of our knowledge, it has not been described in association with pyomyositis. Kikuchi-Fujimoto disease is a benign self-limited ondition that is associated with generalized systemic lymphadenitis and occasionally a low-grade fever.3,4 Commonly, the disease presents with an influenzalike illness and is associated with a rash in 30% of cases.5 We report a case of CA-MRSA pyomyositis with the subsequent development of KFD and transient pancytopenia.

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A 39-year-old previously healthy man presented to the emergency department with complaints of a rapidly expanding left chest wall mass. The patient had experienced low-grade fevers with mild left side of the chest tenderness and weight loss over the previous 2 weeks. The mass was cool and nonfluctuant, leading to an initial suspicion of a malignancy. The lesion expanded from 10 × 4 cm on day 1 to 12 × 6 cm on day 2. A computed tomographic scan of the chest revealed multiple bilateral septic pulmonary emboli and an infiltrative process involving the entire left pectoralis muscle with abscess formation (Figs. 1A, B).



The patient underwent an open biopsy of the mass where a large amount of purulent discharge was drained and cultured. Blood cultures remained negative throughout the hospitalization, but the chest wall drainage grew methicillin-resistant S. aureus. A diagnosis of pyomyositis of the pectoralis major muscle was made. The patient received 6 weeks of intravenous vancomycin with clinical improvement of the pyomyositis.

During the second week of vancomycin therapy, the patient returned to the emergency department with recurrence of fevers and generalized lymphadenopathy. A repeat computed tomographic scan showed enlarged cervical, inguinal, and axillary lymph nodes, with splenomegaly and resolution of the septic emboli in the lungs. The chest wall mass had significantly improved in size and appearance.

The patient also developed pancytopenia that was not present during the previous hospitalization. A bone marrow biopsy demonstrated increased stainable iron but was otherwise normal. A lymph node biopsy was performed and showed evidence of histiocytic necrotizing lymphadenitis or Kikuchi-Fujimoto disease (Figs. 2 and 3). Over the next 3 days, the pancytopenia resolved spontaneously, and the lymphadenopathy resolved within 2 weeks. The patient fully recovered with no further complications.





During the first hospitalization, the hemoglobin level was 13.7 g/dL; platelets, 264,000/μL; and white blood cell count, 11,200/μL, with 72.6% neutrophils and 15.5% lymphocytes. Human immunodeficiency virus 1 and 2 antibodies were negative. Erythrocyte sedimentation rate was 70, and antinuclear antibody screening was positive with an atypical specked Anti-Ro/SSA pattern and a titer of 80. Perinuclear antineutrophil cytoplasmic antibodies and antineutrophil cytoplasmic antibodies with cytoplasmic staining pattern were not detected.

For the second hospitalization, the hemoglobin level was 10.9 g/dL; platelets, 128,000/μL; and white blood cell count, 2800/μL, with 73.7% neutrophils and 18.3% lymphocytes. Toxoplasma and cytomegalovirus serologies (immunoglobulin [Ig] M and IgG) were negative. Human immunodeficiency virus RNA was not detected. Parvovirus IgM was negative, with IgG antibody detected.

Pulse-field gel electrophoresis was performed using Sma I restriction endonuclease and interpreted using standard guidelines. A sample of USA 100, 300, 400, and 800 was compared with our patient's isolate using pulse-field gel electrophoresis. The SCC mec element type and the polymerase chain reaction amplification of the genes encoding Panton-Valentine Leukocidin (PVL) luks-pv and lukf-pv were performed using techniques described elsewhere.6

Staphylococcal chromosomal cassette mec IV was identified in the patient's CA-MRSA. Pulse-field gel electrophoresis demonstrated a band pattern identical to USA 300, and the assay for PVL genes was positive.

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Pyomyositis is a suppurative infection of striated muscle characterized by localized muscle pain, swelling, and tenderness.7 It is hypothesized that pyomyositis initially originates from a transient bacteremia that would not cause clinically evident infection in most individuals. Muscle trauma is thought to be the inciting event leading to seeding of bacteria into the traumatized muscle. Intravenous drug users and immunocompromised patients have been more susceptible to seeding at skeletal muscle sites. Few cases have been described in previously healthy individuals such as our case. Pyomyositis is characterized by 3 distinct stages. These stages are more apparent in untreated patients where the disease may progress to septicemia and death. The mortality rate in tropical regions has been reported as high as 14%.8

During stage 1, patients experience cramps, localized edema, and pain in the infected muscle. Mild leukocytosis and low-grade fever along with a woody texture on palpation are usually present. Aspiration at this stage usually yields little or no discharge.

Stage 2 follows, leading to a frank suppurative stage with abscess formation that occurs 10 to 21 days after symptom onset. Aspiration yields purulent discharge, and up to 90% of patients present in this stage.6 The muscle becomes fluctuant, sometimes warm with little to no skin manifestations over the site of infection. The patient has more severe fever, leukocytosis, and generalized constitutional symptoms of infection.

The septicemic stage of the disease, stage 3, is when dissemination into the bloodstream occurs. Septic emboli along with the formation of multiple abscesses may occur at distant sights. This is the stage we observed in our case.

Cases of CA-MRSA may occur in patients without underlying risk factors, such as intravenous drug use and recent antimicrobial therapy, or associated with a health care facility. Our patient had no exposure to a health care facility and had no known previous infection with S. aureus. Pulse-field gel electrophoresis performed on the chest wall aspirate revealed a band pattern identical to the USA 300 strain of bacteria, and it was SCC mec type IV and PVL (+).

Kikuchi-Fujimoto disease is a rare hyperimmune response to infection, malignancy, or less commonly, drugs.9 The disease usually occurs in the third or fourth decade of life and has a 4:1 female-to-male predominance.10 Kikuchi-Fujimoto disease usually follows a benign self-limited course, but in some cases, it may take many months to resolve.10 There are no previous reports of transient pancytopenia with KFD. Because pancytopenia resolved spontaneously with improvement of KFD in the case above, a possible causal association is surmised.

Consideration of CA-MRSA has become increasingly important when initiating empirical antimicrobial therapy for soft tissue infections in immunocompetent patients and justifies an appropriate diagnostic approach with imaging studies if pyomyositis is suspected.11 Our patient extends the spectrum of clinical manifestations caused by CA-MRSA USA-300 genotype. Prompt diagnosis and therapy with appropriate antibiotics was associated with a successful outcome. Although pyomyositis has been a rare occurrence, to date, KFD has not been reported in association with CA-MRSA.

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