A 31-year-old female with fever and back pain.

Primary pyomyositis is a suppurative infection of striated muscle, the diagnosis of which is overlooked or delayed due to its rarity and vague clinical presentation. Though rare in the United States and temperate zones, pyomyositis is more frequently reported from tropical countries. The exact pathogenesis of pyomyositis is uncertain in most cases. The disease progresses through three stages with characteristic features and require a high index of suspicion to institute stage-wise treatment. Newer imaging methods, particularly magnetic resonance imaging, have facilitated the accurate diagnosis of the infection and of the extent of involvement. Early recognition with appropriate antibiotics in the pre-suppurative stage and prompt surgical intervention in the late stages form the corner stone of treatment. Delay in diagnosis can result in increased morbidity and mortality, especially in diabetics and immunocompromised state. Here, we report a case of primary paraspinal pyomyositis in a middle-aged female and emphasize the importance of early diagnosis and treatment.

INTRODUCTION

Pyomyositis is an acute destructive and suppurative bacterial infection of striated muscle, with paraspinal muscle involvement occurring rarely. The first true description of pyomyositis was given by Scriba in 1885.[1] The diagnosis is often delayed because of the unfamiliarity with the disease, lack of specific signs, atypical manifestations, and a wide range of differential diagnosis. It has predilection for the large muscle masses of the body, with no obvious local or adjacent source of infection. Though predominantly a disease of tropics, there have been reports of pyomyositis from non-tropical countries also.[2] It affects previously healthy individuals and the disease is on the upswing in patients with immunosuppression, acquired immunodeficiency syndrome (AIDS) and diabetes. A high index of suspicion, early diagnosis and intervention are the key principles in the management of primary pyomyositis. A case of primary paraspinal pyomyositis (PPP) in a middle-aged female patient is discussed with emphasis on early diagnosis and treatment.

CASE REPORT

A 31-year-old female presented with fever and back pain of 15 days duration. Her past history was insignificant and she denied any history of trauma, tuberculosis and diabetes mellitus. On examination, the patient was ill looking, febrile with a pulse rate of 96/min. Right lumbar paraspinal region was edematous with local rise of temperature and tenderness [Figure 1]. Fluctuation was absent. Systemic examination failed to reveal a focus of infection elsewhere and there was no neurological deficit in the lower limbs. Laboratory analysis showed hemoglobin 11 g/dl, leukocytosis (20,000/mm3) and raised erythrocyte sedimentation rate (ESR; 100 mm/hour). Liver function tests were within normal limits. Blood urea nitrogen and serum creatinine were within normal limits. Enzyme-linked immunosorbent assay (ELISA) tests for human immunodeficiency virus (HIV) and HBsAg were non-reactive. The peripheral smear revealed reactive neutrophilia with toxic changes in the neutrophils. Urine analysis and culture were unremarkable. X-ray chest and thoraco-lumbar spine was normal. Computerized tomography (CT) showed bulky right posterior paraspinal muscle with heterogeneously hypodense lesion revealing mild peripheral partial rim enhancement with predominantly nonenhancing hypodense center suggestive of abscess formation. The abscess was seen to displace the right kidney anteriorly with maintained fat planes [Figures 2 and 3]. Abscess was drained under anesthesia and the incision closed primarily with a suction drain. Pus culture revealed Staphylococcus aureus, sensitive to flucloxacillin, vancomycin, gentamicin, amikacin and ciprofloxacin. Stain for acid-fast bacilli was negative. Histopathology of the abscess wall showed features of pyogenic abscess with no evidence of tuberculosis. Patient improved with parenteral antibiotics and supportive care, without any residual disability. At 3-month follow-up, the patient remains symptom-free.

Figure 1

Edema of right paraspinal region

Figure 2

Asymmetric enlargement of right paraspinal muscles with abscess formation

Figure 3

Paraspinal muscle abscess displacing the right kidney anteriorly, with maintained fat planes

DISCUSSION

PPP is a rare suppurative infection of striated paraspinal muscles of unknown etiology. Primary pyomyositis (tropical myositis, infective myositis, pyogenic myositis, suppurative myositis, myositis purulenta tropica, epidemic abscess or bacterial pyomyositis) was first described by Scriba in 1885. Though pyomyositis can affect all the muscle groups, it is more common in muscles of the pelvic region and lower extremities. Quadriceps is the most commonly involved muscle, followed by psoas and the upper extremities.[13] Paraspinal muscles are rarely involved (3.8%) and 11-43% of the patients have involvement of multiple sites.[1] PPP is predominantly a disease of the tropical countries, with slight predominance among males (male: female ratio of 5:3). Pyomyositis affects all the age groups with a higher incidence in the first and second decades of life.[4] The rarity of paraspinal pyomyositis is attributed to an assumed resistance of skeletal muscles to bacterial infection.[5] Most patients do not have an obvious portal of entry. Factors like transient bacteremia, trauma and vigorous physical exertion have been described as causative factors in various studies.[3] Patients with diabetes, immunosuppression, malignancy, chronic renal failure, aplastic anemia, leukemia, AIDS, prednisolone therapy, intravenous drug abuse and tropically predisposed circumstances like malnutrition have an increased susceptibility to pyomyositis.[2] Pyomyositis has been well reported in tropical countries where there is often a history of skin trauma which many patients relate to formation of the same. The predominant involvement of right side (dominant side) in tropical pyomyositis might explain this finding.[6] Pyomyositis tends to occur in association with advanced HIV infection or in the presence of an AIDS defining illness. HIV infection increases the risk of multifocal disease, atypical presentation and minimal symptoms because of associated neutrophil dysfunction.[78] With the pandemic of HIV and increased use of post-transplant immunosuppression, there has been a rise in the incidence of tuberculous pyomyositis. Emergence of multidrug resistant strains of tubercle bacilli has resulted in a similar rise among immunocompetent individuals. Tuberculous pyomyositis may present with subtle signs like elevated white blood cell count and ESR. Iliopsoas pyomyositis has been reported in association with tuberculosis and gastrointestinal or kidney infections, which may be the result of direct extension of infection into the muscles from an adjacent focus.[19] The use of immunosuppressive agents masks the symptoms and signs of infection and the disease is usually advanced at the time of diagnosis. Pyomyositis should be differentiated from acute bacterial myositis where the inflammation extends diffusely through the muscle group without distinct abscesses. Acute bacterial myositis is less common than pyomyositis, more frequently involves adult patients and most cases have been due to Streptococcus pyogenes.

PPP occurs deep within the muscles, with intact skin and subcutaneous tissue, and no obvious adjacent source of infection is identified in most cases. Pyomyositis is variably progressive and may take many days or weeks for an infection to become clinically obvious with the end result of a large multiloculated abscess. It may also present as a diffuse inflammatory or a rapidly progressing myonecrotic process.[10]

PPP gradually progresses through three consecutive stages described below.

Stage 1: Diffuse muscle infection – Symptoms are slowly progressive, characterized by dull ache, malaise and a low-grade fever. Absence of local signs of inflammation causes a delay in diagnosis and institution of proper treatment at this stage. Localized signs and symptoms can precede the systemic manifestation by weeks.

Stage 2: Muscle abscess formation – Local manifestations appear with the affected muscle having a firm, wooden texture, and the skin becomes warm and erythematous. The suppurative stage occurs 2-3 weeks after the onset of symptoms. The muscle becomes fluctuant as the disease progresses. Approximately 90% of patients present during the suppurative stage of pyomyositis.

Stage 3: Sepsis – Systemic manifestations and septic shock develop and clinical deterioration begins.[13] This stage requires urgent intervention as the bacteremia results in multiorgan dysfunction.

Pain appears to be the first symptom, and often no other findings are present. Conditions that may mimic PPP include muscle strain, contusion, hematoma, perinephric abscess, osteomyelitis and soft tissue sarcoma. Atypical presentations like pyrexia of unknown origin, acute abdomen, spinal cord compression or compartment syndrome are not uncommon. Regional lymphadenitis is not a routine feature. Physical examination usually reveals scoliosis and a tender mass in the paraspinal region. Routine laboratory evaluation shows leukocytosis with a left shift and an elevated ESR. Though leukocytosis is seen in 70% of the HIV-seronegative patients, it is less common (16.6%) in HIV-positive patients, particularly when the CD4 count is low.[8] Few reports of eosinophilia in association with tropical pyomyositis have been described, but this has not been a constant feature. Serum levels of muscle enzymes and electromyogram are usually normal. These findings help to differentiate pyomyositis from polymyositis. Blood cultures or cultures of purulent material do not reveal the causative organism in most cases. Percutaneous needle aspiration of the involved muscle for detection of pus and providing material for microbiologic isolation can be performed. The most common infectious agent isolated includes St. aureus which causes more than 75% of the cases. Streptococci represent the second most common source. Other agents isolated include Escherichia coli, Salmonella enteritidis, Klebsiella pneumonia, Pseudomonas aeruginosa, Proteus, Yersinia, Haemophilus influenzae, Citrobacter freundii, Morganella morganii, Neisseria gonorrhea and Mycobacterium tuberculosis.[110] More than 95% of staphylococci are resistant to penicillin, and community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) pyomyositis is being increasingly reported in the literature.[1112] Plain radiography is useful for the initial screening to rule out primary bone lesions that mimic PPP. Few patients may have enlargement and loss of definition of the affected muscle, soft tissue gas shadows, and reactive changes in the adjacent bone. Ultrasonography shows a bulky muscle with abnormal echotexture and a hypoechoic focal lesion, occasionally with internal debris and air bubbles.[9] CT provides better delineation of muscle structure and valuable information on the nature and extent of the disease. It also aids in excluding any bony involvement. Specific findings include asymmetric enlargement of the muscle belly, focal area of low attenuation or gas formation and peripheral enhancement after injection of contrast medium. The accuracy of CT is less in children and early stages of infection. Ultrasonography and CT also enable guided percutaneous aspiration and drainage.[113] Magnetic resonance imaging is the preferred modality as it clearly demonstrates diffuse muscle inflammation and is particularly useful in the early stages of the disease. Specific findings include diffuse muscle enlargement with hyperintense rim on enhanced T1-weighted images and an increase in signal intensity on T2-weighted images. Gadolinium enhancement facilitates detection of abscess and makes it the most useful imaging modality in PPP.[13] Gallium scintigraphy is very sensitive and valuable in early detection and localization of occult lesions, especially in patients who do not respond to drainage and antibiotic therapy.[10]

The choice of treatment depends on the stage at presentation. Diffuse muscle infection can be effectively treated with antibiotics alone.[10] Most patients present during the stage of muscle abscess formation and require surgical incision and complete drainage followed by intravenous administration of antibiotics. Drainage can be accomplished percutaneously under ultrasonographic or computerized tomographic guidance if facilities are available. Use of suction drain allows primary closure of the wound after open drainage. Stage of sepsis results due to improper management of stage 2 and requires urgent intervention and immediate administration of antibiotic therapy. Patients in the early stages can be treated successfully with a single antibiotic, while those with sepsis or immunosuppression require combination therapy.[13] Parenteral broad-spectrum antibiotics have to be initiated with coverage for MRSA, especially in susceptible individuals. Antibiotic therapy can be tailored on the basis of the causative pathogen and susceptibility results. The duration of antibiotic therapy depends on clinical improvement. Streptococcal pyomyositis can take a fulminating course with extensive muscle necrosis rather than local abscess formation because of its inherent aggressiveness. It should be differentiated from necrotizing fasciitis which is an infection of the deep soft tissue and is characterized by an extremely tender area that is swol-len and erythematous. Streptococcal gangrenous myonecrosis is associated with more systemic toxicity and a worse prognosis. These cases require radical excision of all the necrotic tissue along with abscess drainage.[114] Possibility of incomplete abscess drainage or multifocal disease should be considered in patients who do not show clinical improvement. Complete recovery without long-term sequelae occurs if the therapy is initiated early. Delay in diagnosis may result in extension of abscess into the retroperitoneum, involvement of spinal elements, sepsis, and occasionally death (<1.5%).[315] Systemic bacteremia can result in endocarditis, myocarditis, pericarditis, myelitis, arachnoiditis, osteomyelitis, renal failure, pneumonia, lung abscess and brain abscess, and few cases of the same have been reported in the literature. Though recurrences and treatment failure rates are low, mortality rate may increase to 15% in neglected and late cases.[111516]

CONCLUSION

The diagnosis of PPP is largely based on the clinical features and the results of imaging studies. External manifestations are lacking in the early stages of the disease. Emergency physicians should become more familiar with this potentially life-threatening but curable entity. Here, we highlight the importance of a high index of suspicion and early therapy in paraspinal pyomyositis as a delay in diagnosis can result in increased morbidity and mortality.