Conjunctival nerve pathology in multiple endocrine neoplasia. A case report

A 31-year-old male with typical clinical features of multiple endocrine neoplasia type 2b (MEN 2b) was subjected to conjunctival biopsy. The patient had previously been operated for pheochromocytoma and medullary carcinoma of the thyroid. He came for ophthalmologic consultation because of redness and irritation of the eye due to dry eye syndrome. The conjunctival biopsy taken from his left eye revealed not only an increase in the number of conjunctival nerves but also an increase of their axons. The ultrastructure of the nerves was mostly normal, but the perineurium was often incomplete, and the interaxonal space appeared to be enlarged. Immunohistochemically, SP-, neurofilament- and, unexpectedly, leucine-enkephalin-positive nerve fibres were demonstrated in the conjunctival stroma. The rat is the only species in which enkephalin-like immunoreactivity has been described in the anterior segment of the eye. Thus, the presence of enkephalin-positive nerves in the conjunctiva of our MEN 2b patient may reflect a profound neural alteration.