Case We report an unusual case of a 63 year old man who developed progressive right-sided exophthalmos, painful ophthalmoplegia, headaches and fevers with worsening depression over a two-month period, subsequently identified as an Actinomyces cavernous sinus (CS) infection. Preliminary diagnoses included giant cell arteritis then Tolosa-Hunt syndrome, with a transient response to steroids. Investigations showed a bland CSF and highly metabolically active brain FDG-PET suggesting lymphoma. Biopsy of the mass demonstrated gram-positive filamentous bacteria with Actinomyces-like colonies with sulphur granules. Actinomyces CS infections are rare. They often mimic non-infectious etiologies including other inflammatory and infiltrative conditions, vascular and neoplastic causes, particularly lymphoma.

Conclusion Clinicians should consider infective CS syndromes in fluctuating painful ophthalmoplegias with poor response to steroids. In our view, “Tolosa-Hunt” should not be used as a diagnosis but merely used as a descriptor for syndromes that resolve with corticosteroids in the absence of a more precise diagnosis.