Necrotizing Soft Tissue Infection of the Thorax Due to Methicillin-Sensitive Staphylococcus aureus Empyem

Abstract

INTRODUCTION: Invasion of the chest wall musculature is a rare complication of empyema. It is often missed or diagnosed late in its course and is associated with high mortality. CASE PRESENTATION: A 51 year-old male with a history of alcoholic cirrhosis presented with fever, cough, dyspnea and pleuritic chest pain. He had been diagnosed with community acquired pneumonia two weeks prior but had failed to fill his antibiotic prescription. On presentation he was afebrile with stable vital signs. He was noted to be jaundiced and had a localized area of erythema with tenderness over his right chest wall. Labs were significant for a leukocyte count of 30K/uL and a total bilirubin of 27mg/dl. A CT scan revealed a large right pleural effusion with compressive atelectasis and edema of the right thoracic soft tissues. Several small foci of air were appreciated within both the pleural effusion and the area of soft tissue edema. Despite the prompt administration of intravenous fluids as well as vancomycin, piperacillin/tazobactam, and clindamycin, the patient developed respiratory failure and septic shock soon after admission to the medical intensive care unit. A chest tube drained 1.5 liters of serosanguinous fluid. The pH of the fluid was 6.5. The patient was evaluated by cardiothoracic surgery and deemed to be a poor candidate for operative intervention. Despite maximal medical therapy the patient expired within 24 hours of admission. His blood cultures grew methicillin-sensitive Staphylococcus aureus (MSSA). Autopsy revealed extensive liquefactive necrosis of the intercostal muscles. DISCUSSION: Empyema rarely results in the development of a necrotizing soft tissue infection. When an extending soft tissue infection occurs it is usually as direct complication of tube thoracostomy or other surgical procedure. A mortality rate of nearly 90% has been reported with this condition, and cure has only been reported after major soft tissue resection including the removal of any involved ribs. The microbiologic agents that have been reported to cause necrotizing soft tissue infection of the chest wall include Bacteriodes fragilis, Clostridium perfringens, Streptococcus pyogenes, Streptococcus milleri, Escherichia coli, and Pseudomonas aeruginosa. This case is unusual in that the patient's necrotizing soft tissue infection of the thorax occurred as a direct result of empyema rather than as a complication of a surgical procedure. It is likely that the patient's prolonged untreated pneumonia and eventual empyema allowed for bacterial invasion from the pleural space into the thoracic soft tissues. To our knowledge, this is also the first reported case of necrotizing soft tissue infection of the thorax caused by Staphylococcus aureus. Although cellulites and localized pyomyositis are commonly caused by this organism, it is a rare cause of necrotizing soft-tissue infection. There have been recent case reports of necrotizing fasciitis as a result of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA). It has been postulated that these cases have resulted from a novel virulence factor expressed by CA-MRSA. The fact that our case was caused by MSSA argues against this theory. CONCLUSIONS: Necrotizing soft tissue infection of the thorax as a direct extension of empyema is a rare and life-threatening entity. Without extensive surgical resection this entity is universally fatal.