Optic Nerve Involvement From Pseudomonas aeruginosa –Associated Skull Base Osteomyelitis

Skull base osteomyelitis (SBO) is an uncommon but life-threatening condition caused by invasive bacterial or fungal infection.¹ Diabetes mellitus, chronic otitis externa, and immunosuppression are frequently associated with SBO.^1,2 More than 60% of patients with SBO are men, and Pseudomonas aeruginosa is the most common bacterial pathogen identified in SBO.^1,2 Cranial nerve palsy most frequently involves cranial nerve VII, followed by the lower cranial nerves (IX-XI).^1,2 We report 2 cases of SBO with rare unilateral optic nerve involvement resulting in no light perception (NLP). These cases highlight the importance of suspecting SBO based on magnetic resonance imaging (MRI), the necessity of a biopsy, and prompt treatment with appropriate intravenous antibiotics.

On February 3, 2009, a 65-year-old healthy man was evaluated for painful visual loss in his right eye for 8 days. The right retro-orbital and scalp pain were unchanged 5 days after treatment with oral prednisone (80 mg/d). Best visual acuity was 20/50 OD and 20/25 OS with a right afferent pupillary defect. The results of the ocular and fundus examinations were otherwise normal. Blood analysis showed a normal erythrocyte sedimentation rate and a normal C-reactive protein level.

The visual acuity in his right eye decreased to 20/400 the next day. An orbital MRI scan showed mild enhancement of the right superior orbital fissure and planum sphenoidalis (Figure 1). The patient was given 1 g/d of methylprednisolone sodium succinate intravenously for 3 days followed by treatment with oral prednisone for 11 days. The patient still reported having extreme pain without visual improvement. The results of a lumbar puncture were normal.

By February 23, 2009, the patient's visual acuity was NLP OD, and he developed right third and sixth cranial nerve palsies. The results of another MRI showed mild, stable enhancement of the right optic nerve sheath with increased enhancement and prominence of soft tissues at the right orbital apex and cavernous sinus (Figure 1). The results of computed tomography of the chest, abdomen, and pelvis were normal.

The results of a biopsy of the right ethmoid sinus were unrevealing, leading to an equally nondiagnostic optic nerve and sheath biopsy. Empirical antifungal therapy resulted in no improvement in pain, vision, or ophthalmoplegia. A transcranial biopsy of the swollen, posterior optic canal dura showed that P aeruginosa grew on the tissue sample, which was observed with hematoxylin-eosin staining (Figure 1). Six weeks of treatment with intravenous meropenem decreased the patient's pain level and decreased his symptoms of ophthalmoplegia, but his visual acuity was NLP OD. The results of an MRI of the brain and orbits 1 week later showed only postsurgical changes.

A 56-year-old man with uncontrolled diabetes and hypertension was hospitalized on June 18, 2011, for excruciating right facial pain and decreased hearing for 1 month. The results of an initial ophthalmic examination were unremarkable, but 1 week later, his visual acuity was NLP OD with total ophthalmoplegia. Ptosis of the right eye and a small nonreactive right pupil were present, with no optic disc edema in either eye. Sensation of the right face was decreased 50% and was worse in the second and third trigeminal divisions. The muscles of mastication were atrophic on the right. The patient had difficulty chewing, and his smile was asymmetric. He developed severe pharyngeal dysphagia, an ineffective cough reflex, and an inability to swallow, which led to the placement of a percutaneous endoscopic gastrotomy tube. In all, there was right optic neuropathy with ipsilateral palsy of the cranial nerves III through XII. The results of an MRI revealed leptomeningeal enhancement of the right temporal skull base and a cavernous sinus extending through the foramen ovale into the infratemporal fossa (Figure 2).

A right temporal craniotomy with extradural biopsy demonstrated a mixture of CD3-positive T cells and CD20-positive B cells that were not malignant. Acid-fast bacilli and Gomori methenamine silver stains were negative for acid-fast bacilli and fungi, respectively. Immunostains were negative for carcinoma and glial tissue. The results of a subsequent nasopharyngeal biopsy were equally nondiagnostic. The results of a C1-C2 cervical puncture revealed normal opening pressure, and the puncture itself allowed for analysis of cerebrospinal fluid samples. An endoscopic biopsy of deeper pharyngeal tissue displayed a few budding yeast forms without tissue invasion, and the tissue sample eventually grew P aeruginosa.

The patient's condition was diagnosed as SBO, and he was given cefepime hydrochloride intravenously. Although the patient's polyneuropathy improved and his visual acuity improved to hand motions after 6 weeks, he was rehospitalized with fever and hyperglycemia, which required that he receive an additional 6 weeks of antibiotics to resolve the symptoms. His visual acuity in the right eye remained hand motions beyond 3 months after treatment but returned to NLP by 8 months.

Skull base osteomyelitis is well reported in the literature, with a few early reports of optic nerve involvement that provide no details of visual function.³ Girkin et al⁴ described a case of P aeruginosa –associated SBO involving the right optic nerve and multiple bilateral cranial nerve palsies in the setting of pachymeningitis. After 4 weeks of intravenous ceftazidime and tobramycin sulfate, the patient's visual acuity in the right eye improved from NLP to hand motions, with resolution of dysphagia and right third and sixth cranial nerve palsies; the left sixth cranial nerve palsy was persistent, and the patient's hearing loss progressed to complete deafness.

Our cases had unilateral involvement of the optic nerve from P aeruginosa –associated SBO without pachymeningitis. Visual acuity progressed to NLP despite treatment and improvement in other cranial nerve palsies. In both cases, findings on MRI scans prompted multiple biopsies; however, we were unable to identify the organisms on pathology. Cultures of the samples from the last biopsy of each case eventually revealed P aeruginosa. This underscores the need for persistence in obtaining tissue to determine diagnosis, assess antibiotic sensitivity, and initiate prompt appropriate intravenous antibiotic treatment, which is essential to preserve the uninvolved optic nerve and reduce mortality.⁵

Suspicion of P aeruginosa –associated SBO is warranted in patients with painful progressive multiple cranial nerve palsies in combination with MRI-detected skull base lesions and/or meningeal enhancement. Although diabetes is a consistent risk factor for SBO, our first patient (case 1) had no diabetes and was not immunocompromised. Vision loss may progress to NLP as early as 1 week after optic nerve involvement, and although empirical therapy is likely beneficial, most cases require at least 6 weeks of appropriate intravenous antibiotics based on antibiotic sensitivity.⁵ Treatment of P aeruginosa –associated SBO must be based on tissue diagnosis, which may require multiple biopsies for pathologic and/or culture confirmation.

Correspondence: Dr Lam, Bascom Palmer Eye Institute, University of Miami Miller School of Medicine, 900 NW 17th St, Miami, FL 33136 (blam@med.miami.edu).

Funding/Support: This work was supported by National Institutes of Health grant P30-EY014801 and an unrestricted grant from Research to Prevent Blindness.