Ocular histopathology in multiple endocrine neoplasia type 2b.

Multiple endocrine neoplasia type 2b is a syndrome, often familial, characterized by medullary carcinoma of the thyroid gland, pheochromocytoma, and many mucosal neuromas in patients who frequently have a marfanoid habitus. The ophthalmic findings are distinctive and include conjunctival and eyelid neuromas, keratoconjunctivitis sicca, and, most characteristically, greatly thickened corneal nerves. Ocular histopathologic study of a 30-year-old man demonstrated thickened nerves in the ciliary body, iris, and corneoscleral limbal regions. In these regions, the nerves were a mixture of myelinated and unmyelinated fibers. Sections through the thickened corneal nerves, 1.5 mm centrally from the corneoscleral limbus, showed only nonmyelinated nerves associated with Schwann cells. The many axons were normal in appearance but varied in diameter; some were between 0.1 and 0.2 ng and others between 1.0 and 1.4 ng. An unexpected finding was numerous ganglion cells in the ciliary body. The subconjunctival tissue showed neuromas with a minimum of fibrous structure. Sections of the lacrimal gland showed normal glandular tissue.