Perineural Invasion of Occult Cutaneous Squamous Cell Carcinoma Mimicking Tolosa-Hunt Syndrome.

We report a case of painful left abducens nerve palsy that progressed to a left cavernous sinus syndrome (CSS). The initial differential diagnosis was Tolosa-Hunt syndrome (THS), but the clinical course was atypical. Subsequently, perineural invasion (PNI) was demonstrated, after biopsy of a previously occult undiagnosed new cutaneous squamous cell carcinoma (SCC) of the forehead. This case emphasizes the challenges of diagnosing painful ophthalmoplegia when there is an absence of positive neuroimaging or typical findings. The take home message is that a detailed medical history and high index of suspicion are necessary in suspected THS.