Endocrine Abstracts

Background: Multiple endocrine neoplasia (MEN) type 2B is an autosomal dominant condition characterised by aggressive medullary C cell tumours, phaeochromocytoma and a discrete physical appearance. A specific point mutation in the RET proto-oncogene is present in 95% cases; prophylactic thyroidectomy is recommended in the mutation carriers. Occasionally cases present with the characteristic physical appearance of MEN2B but no identifiable germline mutation or endocrinopathy (termed ‘mucosal neuroma syndrome’; MNS). Management of such cases remains uncertain.

Case-history: A 13-year-old girl initially presented with photophobia, when she was found to have characteristic features of MEN2B, including prominent corneal nerve fibres, thick lips, multiple mucosal neuromas, marfanoid habitus, high arched palate, ‘coast of Maine’ café au lait patch and genu valgum. Blood pressure was 120/65 mmHg. Initial investigations showed normal 24-hour urinary catecholamines, serum calcium, parathyroid hormone, basal and alcohol stimulated calcitonin (<0.08 mcg/l), and CT of the adrenal glands. She was followed up with regular urinary catecholamine and pentagastrin stimulated serum calcitonin levels. Pentagastrin stimulation 18 months after presentation gave equivocal results. Baseline calcitonin level was 0.09 mcg/l (normal<0.08 mcg/l), rising to a peak of 0.14 mcg/l at 2 minutes. Because of the uncertainty surrounding the natural history of patients presenting with this phenotype at a time when the gene was unknown, in association with a rise in basal calcitonin, a decision was made to proceed to prophylactic thyroidectomy. Histology showed no evidence of medullary carcinoma or C cell hyperplasia. Recently sequencing of exons 10, 11, 13, 14, 15 and 16 of the RET gene showed no mutation. The patient has been followed up annually for the last 18 years and has remained well.

Conclusions: This case suggests that mandatory prophylactic thyroidectomy is unnecessary in patients with MNS without RET mutation or endocrinoapthy, although they should be screened for endocrinopathy on a regular basis.