Enigmatic trigeminal sensory neuropathy diagnosed by facial skin biopsy.

Facial paraesthesia due to perineural malignant infiltration is a well recognised complication of basal and squamous cell carcinomas of the head and neck. Perineural involvement was originally attributed to involvement of the perineural lymphatics; however subsequent studies have demonstrated conclusively that these lymphatics do not exist and that the invasion occurs along the line of least resistance. Previous studies on perineural spread of carcinomas of the head and neck have emphasised diagnostic biopsy of an involved nerve (e.g. the infraorbital, mental or major branches of the trigeminal nerve), or at times craniectomy with exploration of the gasserian ganglion. We suggest that in many cases the diagnosis can be obtained by biopsy of the anaesthetic skin alone, without recourse to more involved biopsy techniques. The following case report illustrates this point.