Serratia Marcescens Sinusitis Presenting as Left Orbital Apex Syndrome

Orbital apex syndrome (OAS) is a vision-threatening condition characterized by optic neuropathy, ophthalmoplegia, and cranial nerve dysfunction at the orbital apex. While fungal and neoplastic aetiologies are well recognized, bacterial causes are uncommon. Serratia marcescens, an opportunistic Gram-negative bacillus primarily associated with nosocomial infections, has rarely been implicated in sinusitis or orbital apex involvement.

A 73-year-old woman with type 2 diabetes presented with progressive unilateral headache, diplopia, and vision loss. She was empirically treated for allergic and bacterial sinusitis, including steroids, without improvement. Imaging showed left sphenoethmoid sinus opacification with orbital apex involvement, and initial endoscopy suggested fungal sinusitis. Repeat biopsy ruled out fungal disease and malignancy, while cultures identified S. marcescens susceptible to cephalosporins and fluoroquinolones. Antifungals were discontinued and completed levofloxacin with rapid clinical recovery. At 2-month follow-up, imaging confirmed resolution of orbital apex inflammation and sinus disease.

This case highlights S. marcescens as a rare cause of OAS in the setting of sphenoid sinusitis. Awareness of atypical bacterial pathogens, avoidance of premature steroid or antifungal therapy, and reliance on repeat endoscopy with cultures are critical for timely diagnosis and vision preservation.

In immunocompromised patients presenting with orbital apex syndrome, the differential diagnosis should be broadened to include rare Gram-negative pathogens.Repeat endoscopy and biopsy are essential in atypical, progressive, or refractory cases.Serratia marcescens should be recognized as a potential emerging pathogen beyond its traditional nosocomial associations.