A 67-year-old white man presented, in 2010, with 6 weeks of double vision and left-sided periorbital pain with altered sensation. There was an incomplete third nerve palsy and altered sensation in the first and second trigeminal dermatomes. A malignant melanoma had been excised from his right forearm in 2003, with negative sentinel axial lymph node biopsy. In 2006, he had developed bilateral submandibular salivary gland enlargement, which histologically was chronic inflammatory sialadenitis.

Plasma viscosity was persistently raised at 2.28 mPa/s (1.5–1.72) but serum C-reactive protein and serum ACE …