Pseudomonas aeruginosa (P. aeruginosa) is a Gram-negative bacillus that may be the etiological agent of mild to severe skin conditions, such as folliculitis, erysipelas, digital intertrigo, green nail syndrome, ecthyma gangrenosum, and sepsis.1 In immunosuppressed and hospitalized patients, P. aeruginosa often behaves as an opportunistic pathogen and frequently causes septicemia, abscesses, and wound infections.2 Subcutaneous nodules constitute a rare manifestation, and most published case reports did not include a full laboratory investigation, providing limited information on this disease.3,4 The present report describes a patient with panniculitis caused by P. aeruginosa, with a literature review.

A 44-year-old female patient, diagnosed with systemic lupus erythematosus (SLE), using prednisone 1 mg/kg/day as an immunosuppressant drug, was admitted to the Rheumatology ward for treatment of gastroenterocolitis and uveitis caused by cytomegalovirus with ganciclovir. During hospitalization, the patient had a P. aeruginosa bloodstream infection, which was resolved after treatment with meropenem 2 g every 8 hours for ten days. After one month, a dermatology consultation was requested due to the appearance of erythematous nodules on the upper back, thorax, face, upper limbs and breasts (Figs. 1 and 2), without other systemic symptoms.

Figure 1.

Hyperchromic nodules on the upper thoracic region and left upper limb.

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Figure 2.

Hyperchromic nodules on the left upper limb.

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A punch biopsy was performed on the upper back lesion. The histopathological examination showed a neutrophilic infiltrate in the dermis, associated with suppurative folliculitis that extended to the hypodermis (Figs. 3 and 4). There were no significant findings in the other exams, including the blood culture.

Figure 3.

Histopathological examination revealed the presence of a lobular inflammatory infiltrate in the hypodermis (Hematoxylin & eosin, ×100).

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Figure 4.

At higher magnification, the histopathological examination revealed the presence of a neutrophilic infiltrate in the hypodermis (Hematoxylin & eosin, ×400).

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In the skin culture, P. aeruginosa was isolated with an antimicrobial resistance profile identical to that of the bacteria that had been previously obtained in the peripheral blood culture at the time of the bloodstream infection. With these findings, the diagnosis of infectious panniculitis caused by P. aeruginosa was confirmed, and after treatment with ciprofloxacin 500 mg, every 12 hours for 4 weeks, the lesions improved without recurrence.

Erythematous nodules on the limbs and trunk can occur in SLE, erythema nodosum, type 2 leprosy reaction, erythema induratum of Bazin, nodular vasculitis, and infectious, traumatic, or insulin-induced panniculitis. Erythema nodosum is the most frequent cause of panniculitis, although in patients diagnosed with SLE, lupus panniculitis or lupus profundus may occur in approximately 1%–3% of these patients.5

The anatomopathological examination with neutrophilic infiltrate without vasculitis in the hypodermis is characteristic of pancreatic panniculitis, panniculitis associated to alpha-1-antitrypsin deficiency, and infectious panniculitis.5 In infectious panniculitis, the microorganisms can be identified using special staining methods, such as hematoxylin-eosin, Gram or Ziehl-Neelsen, and the identification of the agent is performed through immunohistochemistry, serology or biopsy culture, with the latter being the gold standard for diagnostic confirmation.6

P. aeruginosa is commonly found in humid environments and in the human intestinal flora. This microorganism can cause both community-acquired and nosocomial skin infections through direct inoculation, hematogenous spread, or intestinal translocation.1 Immunosuppression or local alterations in immunity predispose to sepsis, with increased mortality in the hospital environment due to the existence of a multidrug-resistant P. aeruginosa strain.2

There are only six reports of panniculitis caused by P. aeruginosa in the literature with the description of clinical, histopathological, and microbiological diagnoses (Table 1). 7–10 The patients mean age was 65.1 years (50–80 years), predominantly females (n = 5), and all of them were immunosuppressed (n = 4 over 60 years old, n = 3 with diabetes mellitus, n = 1 with liver cirrhosis, n = 2 undergoing chemotherapy). Regarding the clinical picture, the patients had erythematous nodules, predominantly on the lower limbs, some of which were ulcerated. Three cases had skin lesions accompanied by sepsis, and in two cases, P. aeruginosa was isolated from the bloodstream.

This is the first report of panniculitis caused by P. aeruginosa with confirmatory clinical, histopathological and microbiological examinations in a patient with SLE. As reported, the patient was immunosuppressed and had a previous episode of septicemia caused by P. aeruginosa. The hypothesis of the present case is that the patient was colonized by P. aeruginosa and that, through hematogenous dissemination, this microorganism reached the hypodermis and triggered the formation of multiple subcutaneous nodules. The importance of considering infectious panniculitis as a differential diagnosis in immunosuppressed patients is emphasized, even in the absence of fever or other signs of sepsis. Early identification and adequate treatment with antibiotics can improve the prognosis of these patients.

None declared.

Tatiana Mina Yendo: Patient follow-up; manuscript preparation.

Cristina de Castro Pante: Patient follow-up; manuscript preparation.

Denise Miyamoto: Manuscript review.

None declared.