Seton Infection: Serratia Marcescens:

57-year-old white female with 1 day history of redness, swelling, and pain in her right eye

Seton Infection: Serratia Marcescens:

57-year-old white female with 1 day history of redness, swelling, and pain in her right eye

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Chief Complaint: 57-year-old white female with 1 day history of redness, swelling, and pain in her right eye.

Ocular History:

• Aphakia: Cataract extraction OD 1982, OS 1980
• Scleral buckle OD 1989
• Aphakic glaucoma OU: No light perception (NLP) OS
• Trabeculectomy with mitomycin C (MMC) OD 4/10/01
• Ahmed seton implant OD 4/25/01
• Rigid gas permeable contact lens OD

Medical History: Emphysema, angina, diverticulitis, gallstones, GERD

Ocular Exam:

• Vision without correction: OD: hand motions (Baseline 20/125, best corrected visual acuity), OS: NLP (end-stage glaucoma)
• IOP: 22 mmHg OD and OS
• Hertel exophthalmometer: Proptosis OD (19 mm OD, 16 mm OS, Base 102)
• Motility: OD: -3 limitation all fields of gaze
• Slit lamp exam OD: chemosis and significant conjunctival injection, Ahmed valve and scleral buckle in place (Figure 1A). No evident exposure of either element. Of note, the anterior chamber was deep and quiet with no cell nor flare.
• Fundus OD: clear view, no vitreous cell, 0.9 C:D (see Figure 1B)

Figure 1

1A: Slit lamp view of the injected, chemotic conjuntivae overlying the Ahmed device, OD.	1B: Fundus, OD. Large cup to disc ratio, but no vitreous cell and otherwise normal fundus. (The yellow crescent is photographic artifact).

Labs: Complete blood count (CBC) and metabolic panel were both normal. Blood cultures were negative.

A painful, red, proptotic eye led us to be concerned about infection. Suspecting involvement of the glaucoma drain (implanted seton), a B-scan (echo) of the orbit and lids was performed, OD. This showed a bleb twice the normal size filled with turbid fluid (see Figure 2).

Figure 2: A-scan (echo) of the orbit, OD.

A computed tomography (CT) scan of the orbit and sinuses was performed and is shown in Figure 3.

Figure 3: CT orbit, non-contrast, axial view. Periorbital swelling and fat stranding is clearly evident around the right eye, adjacent to the Ahmed drain. Sinuses are clear.

Discussion

Our patient presented with acute red eye, pain and decreased vision. Clinical picture, combined with echo and CT scan of the orbit, confirmed a diagnosis of orbital cellulitis associated with the Ahmed seton, and possibly the scleral buckle. In this case, there was no associated intraocular infection.  Broad-spectrum  intravenous antibiotics (vancomycin and ceftriaxone) were started with prompt surgical removal of the Ahmed seton and scleral buckle on the day of presentation. 

Mucopurulent material found upon opening the tenons capsule around the seton bleb was drained and sent for culture. Gram stain initially revealed gram negative bacilli (see Figure 4) and cultures grew Serratia marcescens from both her extracted seton and scleral buckle element. Some colonies of Enterococcus grew from samples of the scleral buckle only.

Figure 4: A Gram stain (500x magnification) of the purulent material isolated at the time of seton and scleral buckle removal shows gram negative bacilli, later identified as Serratia marcescens on culture.

Serratia marcescens has been identified as the causative agent in lacrimal duct infections, conjunctivitis, keratitis, and endophthalmitis.  Frequently, the infection has been associated with systemic risk factors such as diabetes mellitus, renal failure, alcoholism, and rheumatoid arthritis. S marcescens can be found not uncommonly in the respiratory and urinary tract in adults and within the gastrointestinal system of young children.  S marcescens ocular infections have been associated with contact lens wear, especially rigid gas-permeable contact lenses and previous eye surgery. 

Enterococcus, the second organism cultured from the scleral buckle, is a part of the normal fecal flora and can cause eye infections including endophthalmitis, orbital cellulitis from sinus disease, and keratitis.  It is an uncommon cause of scleral buckle-related infection.  In one case series from Bascom Palmer, Enterococcus (Streptococcus fecalis) was found in only 6% of positive cultures.

In our patient, there were no identifiable systemic risk factors.  However, her ocular risk factors included contact lens wear and previous eye surgeries. In this case, the patient's contact lens was suspected as the source of infection, and we were able to culture Serratia directly from it.  It is unclear how the organisms gained access to the seton and bleb without evidence of a breach of the conjunctiva.  It is possible that use of mitomycin C may have thinned the conjunctiva over the seton bleb facilitating microbial access.  Despite severe orbital infection, there was no sign of endophthalmitis (as witnessed by clear anterior chamber and clear vitreous media noted in the exam above).  This is consistent with the idea that the Ahmed seton functions like a one-way valve and does not allow backflow from the orbit into the eye.

The treatment of S marcescens ocular infection is challenging because the organism is multi-drug resistant.  Aminoglycosides and amikacin both show consistent efficacy in vitro.  Third generation cephalosporins, fluoroquinolones, trimethoprim/sulfamethoxazole, tetracycline, and synthetic penicillins show more variable activity.  In our patient, IV ceftriaxone followed by a 2 week course of oral levofloxacin was effective (post-operative image in Figure 5).  Antibiotic resistance is also a problem in the treatment of Enterococcus, but vancomycin is frequently effective.

S marcescens is a rare cause of orbital cellulitis, but a potentially sight-threatening one if it is not detected early and treated aggressively. A high index of suspicion and prompt managment can lead to good visual outcomes.

Figure 5: Post-operative view, OD. Eye is quite and well-healed.

Diagnosis: Serratia Marcescens orbital cellulitis associated with glaucoma seton implant

EPIDEMIOLOGY Systemic risk factors: diabetes mellitus, renal failure, alcoholism, and rheumatoid arthritis Ocular risk factors: contact lens wear (especially rigid gas-permeable contact lenses) and previous eye surgery

SIGNS Proptosis Chemosis Conjunctival injection Decreased motility CT: fat stranding, periorbital swelling ECHO: collection of turbid fluid

SYMPTOMS Pain Redness Decreased vision Mucopurulent discharge

TREATMENT S marcescens is frequently multi-drug resisant Aminoglycosides and Amikacin show consistent efficacy in vitro Third generation cephalosporins, fluoroquinolones, tetracycline, trimethoprim/sulfamethoxazole, and synthetic penicillins show more variable activity In our patient, IV ceftriaxone followed by a 2 week course of oral levofloxacin was effective Antibiotic resistance is also a problem in the treatment of Enterococcus, but vancomycin is frequently effective

Differential Diagnoses

• Preseptal cellulitis
• Orbital Cellulitis
• Seton implant infection
• Endophthalmitis