Septic pulmonary embolism associated with a peri-proctal abscess in an immunocompetent host

Abstract

Septic pulmonary embolism is an uncommon disease in which septic thrombi are mobilised from an infectious nidus and transported in the vascular system of the lungs. It is usually associated with tricuspid valve vegetation, septic thrombophlebitis or infected venous catheters. We report an immunocompetent young man who presented with fever and pleuritic chest pain. Chest roentgenography and CT showed multiple ill-defined nodules, with central cavitation and feeding vessels. He was found to have a clinically infectious source of methicillin-resistant staphylococcus aureus (MRSA) cultured from the peri-proctal abscess with the same bacteraemia. Pulmonary septic embolism from peri-proctal abscess was diagnosed by image study and bacterial culture correlation. All of the clinical presentations improved after the incision of the peri-proctal abscess and anti-MRSA antibiotics treatment.

BACKGROUND

Septic pulmonary embolism is a rare clinical presentation and a difficult diagnosis. We presented an unusual cause of septic pulmonary embolism from skin infection and where the pulmonary embolism resolved after successful treatment of the infectious focus.

CASE PRESENTATION

A 35-year-old, single, Chinese male, who worked as a mechanic in a bicycle factory, presented with fever off and on for 4 days. He was in good health and denied having any previous disease. There was no trauma, recent travel or history of drug abuse. He found a carbuncle on his right buttock 1 week before admission. Fever and progressive dyspnoea occurred 4 days before admission to hospital. Two days before admission, left-sided chest pain following deep breathing presented. There were no respiratory symptoms except for dyspnoea.

INVESTIGATIONS

At initial presentation, body temperature was 38.1°C. His blood pressure was 90/65 mmHg, respiratory rate was 25 breaths per minute and pulse was 93 beats per minute. Physical examination showed a tender, hard, mass over his right buttock with pus discharge. Lung and heart auscultation disclosed normal findings. There was no Osler node, Janeway lesions or other haemorrhage or echymosis lesions on his skin. His white blood count was 17800/mcL with left shift. The c-reactive protein was 11.58 g/dL. Arterial blood gas analysis revealed pH 7.5, PaCO₂ 29.7 mm Hg and PaO₂ 82.1 mm Hg while breathing room air. Chest radiography showed multiple ill-defined nodular lesions over the bilateral lung field (fig 1). Chest CT showed multiple different-shape nodules on both lungs—some of them had central low attenuation, feeding vessels and wedge-shaped lesions abutting to pleura (fig 2). Transthoracic echocardiograms did not demonstrate any vegetation on cardiac valves. After conducting a detailed search, no other infectious sources were found except for peri-proctal abscess.

Figure 1.

Chest radiography showing bilateral and peripheral multiple well-defined pulmonary nodules.

Figure 2.

CT of the chest demonstrating the peripheral nature of pleural-based nodules (black arrow), relatively well-defined margins and a variable degree of cavitation.

TREATMENT

Oxacillin was given initially and then later vancomycin due to positive findings of methicillin-resistant staphylococcus aureus (MRSA) cultured from peri-proctal abscess and blood. Due to the high mortality rate (49.8%) in MRSA sepsis,¹ emergent surgical incision and drainage of the peri-proctal abscess (fig 3) was performed. There was no rectal fistula.

Figure 3.

The patient received emergenchy surgical incision and drainage of peri-proctal abscess.

OUTCOME AND FOLLOW-UP

After 3 weeks of vancomycin treatment, the patient showed significant clinical improvement as well as the septic pulmonary lesion on chest radiography. Serum c-reactive protein concentration returned to the normal range. No immunodeficiency condition was noted after the admission to hospital investigation, including a negative HIV test.

The immunocompetent patient discharged with a 2-week full course of vancomycin treatment. After 6 months of follow up, the patient did not suffer a recurrence of community-acquired MRSA soft tissue infection with septic pulmonary lesions.

DISCUSSION

Septic pulmonary embolism arising from peri-proctal abscess was highly suspected and, therefore, antibiotics were administered and surgical intervention for abscess debridement was performed. The abscess grew MRSA. To the best of our knowledge, this is the first reported case of pulmonary septic embolism regarding peri-proctal abscess.

Septic pulmonary embolism is an uncommon disease in which thrombi containing microorganisms in a fibrin matrix are mobilised from an infectious nidus and transported in the venous system to implant in the vascular system of the lungs. It is usually associated with tricuspid valve vegetation, septic thrombophlebitis or infected venous catheters.² Less common infection with the potential for septic pulmonary embolism is postanginal septicaemia, sometimes referred to as Lemierre’s syndrome,³ and periodontal disease.⁴

Chest CT played an important role in the diagnosis of pulmonary septic embolism. In a review study by Kuhlman et al of 18 patients,⁵ CT features of septic embolism included the presence of multiple peripheral nodules (n=15, 83%) ranging in size from 0.5– 3.5 cm. A predominantly basilar distribution was evident in 11 of 18 patients (61%), cavitation of nodules presented in 9 of 18 patients (50%) and air bronchograms were identified within pulmonary nodules in 5 of 18 patients (28%). Cook et al in 2005 showed non-specific clinical and radiographic characteristics in the diagnosis of pulmonary septic emboli. However, CT findings of multiple nodular lung infiltrates peripherally, with or without cavitation, could help the diagnosis.²

We could not find another infectious focus except for the peri-proctal abscess. Establishing the diagnosis and the relationship between the infectious peri-rectal abscess and pulmonary septic embolism is difficult; however, we have strong evidence that both the abscess and blood culture grew the same pathogen of MRSA. This is an unusual case of pulmonary septic embolism compared with previous reports.^2–4 One possible explanation is that the septic pulmonary embolism was caused by the MRSA sepsis following a community-acquired MRSA soft tissue infection.

LEARNING POINTS

• Septic pulmonary embolism can be caused by a skin abscess.

• Emergent debridement of skin abscess and appropriate antibiotics can be the effective treatment of pulmonary embolism.