Case Presentation: A 68 year old man with history of polyarteritis nodosa on azathioprine/prednisone presented with four months of headache, hearing loss, and encephalopathy. Work-up included CT and MRI head/neck which revealed an ill-defined soft tissue mass within the posterior nasopharynx, extending into adjacent bony structures with areas of focal lytic destruction, concerning for malignancy. Besides elevated CRP/ESR, blood and CSF studies were negative. Biopsy of the mass preliminarily suggested lymphoma and patient was discharged with oncology follow up; however, final results showed only chronic inflammation without malignancy. Progressive symptoms prompted readmission, again with elevated CRP/ESR but otherwise negative work-up. A second biopsy of the mass showed only focal fibrosis suggestive of prior biopsy. Subsequent studies included WBC scan, which showed no abnormal uptake to suggest infection, and PET/CT scan which showed marked FDG activity associated with the mass, “consistent with neoplasm” per report.After interdisciplinary team discussions, ENT performed a third biopsy of the mass, this time also obtaining a sample of the clivus. Bone culture ultimately grew Pseudomonas aeruginosa, Kocuria kristinae, and MRSE, confirming diagnosis of osteomyelitis. IV ceftazidime was started, then broadened to daptomycin and meropenem. Repeat MRI brain showed mild improvement in bony involvement and stable to slightly improved abnormal soft tissue. He completed 6 weeks of IV antibiotics with improvement in cognition, downtrending CRP/ESR, and resolution of headache. He remains on suppressive therapy with PO levofloxacin.
Discussion: Skull base osteomyelitis (SBO) is a rare, potentially fatal disease. Typical cases of SBO are due to Pseudomonas aeruginosa, involve the temporal bone, and are a complication of otitis externa in immunocompromised patients. Central skull base osteomyelitis (cSBO) is even rarer and involves the sphenoid or occipital bone, often the clivus, without preceding otitis externa. cSBO can present with only headache; facial pain and cranial nerve deficits can also occur, but fever is uncommon. MRI findings involve clival bone marrow T1 hypointensity and preclival soft tissue infiltration. Even with treatment, mortality rate is 10-20%, with long-term neurologic sequelae in up to 31%. Treatment is with antibiotics for 1-6 months; in some cases, adjuvant hyperbaric oxygen or surgical debridement is used.
Conclusions: cSBO is a difficult diagnosis to make, as biopsies may show only non-diagnostic inflammation, and lytic bone destruction and soft tissue involvement on imaging may lead to incorrect diagnosis of malignancy. In this case, inability to confirm cSBO by obtaining a bone sample delayed treatment by weeks. Obtaining appropriate tissue samples is critical for correct diagnosis of cSBO and it should remain on the differential for immunosuppressed patients presenting with headache and classic MRI/CT findings, even in the absence of sepsis.