Case Presentation: A 3 year old girl with no significant past medical history presented with fever of unknown origin (FUO). Ten days prior to hospital presentation she began having daily fevers with mild URI symptoms. She developed abdominal pain, was diagnosed with a UTI by urinalysis, and was started on cephalexin by her primary pediatrician. She was switched to cefixime for persistent pain and fevers; however, the original urine culture was ultimately negative. Given daily fevers without clear source, she was admitted for evaluation of FUO. Her admission labs were remarkable for leukocytosis without left shift and substantially elevated CRP and ESR. An abdominal ultrasound was negative for appendicitis and a CT abdomen and pelvis was nondiagnostic. A lumbar puncture performed for neck stiffness was unremarkable. Her fevers resolved and CRP began to decrease. Three days after admission she developed snoring and intermittent bilateral esotropia, her ESR remained elevated, and she had poor oral intake so a brain MRI was performed. Imaging was remarkable for a clival osteomyelitis, adjacent retroclival and retropharyngeal abscesses (RPA), and fluid in the mastoid air cells with thickening of the sinuses. ENT drained the RPA. Abscess culture grew MSSA so she was transitioned to intravenous (IV) ampicillin/sulbactam. One week after starting IV antibiotics, a repeat MRI demonstrated full resolution of the osteomyelitis. She was treated with three weeks of IV antibiotics and one week of oral antibiotics. At follow up she was in her usual state of health. 

Discussion: The cause of FUO can be difficult to identify in young patients as they may struggle to describe symptoms; hence, it is important to reevaluate the differential diagnosis as new signs emerge. Consider obtaining an MRI in a FUO patient that develops bulbar signs as clival osteomyelitis is a rare diagnosis with significant complications making early identification and treatment paramount.

Conclusions: Clival osteomyelitis is found predominantly in elderly and immunocompromised patients, but has been described in children. It is likely caused by extension of a sinusitis or otitis media. This skull base osteomyelitis is usually only recognized after neuroimaging because it presents with vague symptoms; therefore, clinicians must carefully watch a patient’s physical exam and have a low threshold to evaluate with MRI or CT. In our patient snoring was likely secondary to mass effect of the RPA, and esotropia was due to bilateral VI nerve palsies as these nerves course over the clivus. Cranial nerves IX, X, and XII can also be affected in clival osteomyelitis and older individuals may complain of headaches and dysphagia. Other complications of skull base osteomyelitis include meningitis, intracranial abscesses, sinus venous thrombosis, and carotid artery involvement; thus, prompt treatment of this condition is critical.