Scedosporium and Cutibacterium skull base osteomyelitis complicated by blindness from fulminant papilloedema

A 48-year-old Pacific man with a background of diabetes developed chronic right otitis with mastoiditis in 2016 and underwent a modified radical mastoidectomy in 2018. Post-operatively he developed skull base osteomyelitis (SBO) and dural venous sinus thrombosis diagnosed with computed tomography (CT) with venogram. In 2020 his vision deteriorated with severe papilloedema and he was referred to our centre.

On review he had thick, green ear discharge and warm, non-tender swelling behind the right ear. Visual acuity was hand movements in right eye and no light perception in left eye. Ocular examination showed bilateral end-stage pallid optic disc swelling and bilateral retinal central retinal vein occlusions (Figure 1), without retinal ischaemia.

View Figure 1–2.

Full blood count showed mild neutrophilia. Glycated haemoglobin was 53mmol/mol (reference range <41mmol/mol) and C-reactive protein was 26mg/L (reference range <6mg/L). Superficial swabs from the right ear canal grew two yeasts identified as belonging to the Candida parapsilosis complex, thought to be commensal flora.

A follow-up CT with venogram showed the right mastoidectomy, mastoid air cell opacification, sclerotic and erosive changes affecting the right petrous temporal bone, sphenoid bone and clivus, and soft tissue inflammation including subgaleal collection. Right transverse and sigmoid sinus thrombosis was demonstrated.

Sterile subgaleal collection aspirate showed leukocytes but no organisms on Gram stain (no additional stains used), and grew environmental fungus Scedosporium apiospermum, sensitive to voriconazole with minimum inhibitory concentration 0.5mg/L.

An MRI showed extra-axial enhancing soft tissue along the inner aspects of right occipital and temporal bones, extending into the posterior and middle cranial fossae. Soft tissues in the scalp and neck were oedematous and enhancing (Figure 2). Lumbar puncture opening pressure was >38cmH₂O. Cerebrospinal fluid analysis showed 48x10⁶/L white cells (97% mononuclear) with raised protein and normal glucose. No organisms were isolated following extended incubation.

A multidisciplinary team including infectious disease, otorhinolaryngology, ophthalmology and neurosurgical specialists managed this case. Oral voriconazole 200mg BD and terbinafine 250mg daily were commenced with monitoring of serum levels and liver function. Oral acetazolamide 250mg TDS continued for 8 months to reduce intracranial pressure. Ventriculoperitoneal shunt was deemed inappropriate due to active extra-axial infection. Right optic nerve sheath fenestration was conducted to protect remaining vision: optic disc oedema resolved quickly but remaining light perception in the right eye was gradually lost.

Neuroimaging over the following year showed gradual improvement. Terbinafine was discontinued after 12 months due to increasing cholestatic liver enzymes. Subsequently, right-sided headaches recurred with neutrophilia and increased C-reactive protein (39mg/L). A CT demonstrated increased temporoparietal lobe oedema and extracranial soft tissue inflammation. Another sterile deep tissue biopsy was taken, including deep fascia, occipital bone and extradural tissue. Cutibacterium acnes was grown from bone and fascia. Oral doxycycline 100mg BD was initiated for possible bacterial coinfection given excellent bony penetrance, with gradual clinical improvement. He received 26 months of antifungal treatment and 12 months of antibacterial treatment.

Skull base osteomyelitis is a rare and dangerous infection spreading from otological or sinus infections, typically caused by Pseudomonas aeruginosa with malignant otitis externa.^1,2,3 S. apiospermium is a ubiquitous fungus that most commonly causes infection in immune-compromised patients.⁴ C. acnes has also been reported to be the causative organism in a small number of SBO cases complicated cranial neuropathy.⁵ The facial nerve is the most implicated cranial nerve in SBO due to its course through the stylomastoid foramen.⁶ Optic nerve involvement is much less common, and in this case the involvement was indirect through intracranial hypertension. The case highlights important aspects of SBO, particularly 1) external ear swab results can be misleading, especially after antibiotic treatment;⁷ 2) a prolonged relapsing course from treatment failure is well recognised;⁸ thus 3) sterile-site microbiological samples should be prioritised in the workup of SBO, after 48 hours without antimicrobials; and finally 4) among the catastrophic complications of SBO, this is the first report of intractable blinding papilloedema despite optic nerve sheath fenestration.⁹