Case 5 -

MEN 2B Dr. C. W. Chow Royal Children's Hospital Melbourne, Australia

Case History: This male baby was born at term by lower segment Caesarian section after breech labour. He was referred from a peripheral hospital to the Royal Children's Hospital on day 13 following abdominal distension, vomiting and 10% loss in weight. Suction rectal biopsy was performed. Acetylcholinesterase showed a prominent submucosal plexus, but the coarse discrete cholinergic nerve fibres in the muscularis mucosae typical of Hirschsprung's disease were not seen. Case 5 - Slide 1 Click to view with ImageScope Click to view with a Web-Based Viewer Case Report: This male baby was delivered at term by lower segment Caeserian section following breech labour. He was admitted from a peripheral hospital on day 13 following vomiting, weight loss of 10% and abdominal distension. Suction rectal biopsy showed prominent bundles of nerve fibres and clusters of neurons in the submucosa. These occupy in some sections 1/3 of the submucosal area. Acetylcholinesterase showed no coarse discrete fibres in the muscularis mucosae. Hirschsprung's disease was excluded but the significance of the hypertrophied submucosal plexus was unclear. Intestinal ganglioneuromatosis was considered. However family history showed that the maternal great grandfather had a lock of white hair and the maternal grandfather had green iris in one eye and brown iris in the other. Mother was normal. In view of this it was felt that perhaps the changes were related to a form of Waardenberg syndrome. Although the typical lesion of Waardenberg syndrome is Hirschsprung's disease an occasional report described decreased or increased neurons [1]. In spite of repeated bowel washouts, there was increasing abdominal distension. Barium meal showed malrotation. A Ladd's procedure and a colostomy were performed. At the time of surgery, the appendix and a seromuscular biopsy of the small intestine were removed, both showing marked hypertrophy of the myenteric plexus, typical of diffuse intestinal ganglioneuromatosis. Although there was still uncertainty about the cause of the lesion, it was decided to check the possibility of MEN 2B first, as this was the easiest to arrange. Molecular studies showed a germline Met918Thr mutation of the RET proto- oncogene. No mutation was detected in the parents. Follow-up studies at 8 months showed that serum calcitonin level was 270 ng/L(normal <30). Thyroid ultrasound revealed a 4mm solid nodule in each lobe. The adrenals showed no abnormality. A total thyroidectomy was performed one month later. Histopathology showed 2 well-circumscribed but non-encapsulated nodules composed of solid clusters of polyhedral to spindle tumour cells supported by a delicate vascular stroma. The nuclei were regular, round to oval with fine even chromatin. The cytoplasm was finely granular and eosinophilic. Immunohistochemistry showed that the tumour cells were positive for calcitonin. The features were those of multifocal medullary thyroid carcinoma. Post-operative follow-up 15 months later showed that the boy continues to thrive with the colostomy. Calcitonin levels were not elevated. Metastases were not found. Discussion: Suction rectal biopsies are often performed in infants and children with intestinal obstruction for the diagnosis of Hirschsprung's disease, either by the absence of ganglion cells in the submucosa, or by the presence of many coarse discrete cholinergic fibres in the muscularis mucosae [2]. After Hirschsprung's disease has been excluded, there does not appear to be any uniform policy for further investigations. There are various new studies including immunohistochemical demonstration of neuropeptides such as substance P, vasoactive intestinal peptide and nitric oxide synthase, physiologic studies in organ baths, multichannel colonic manometry, and nuclear transit studies [3]. These are still at the research stage and there do not yet appear to be easily used diagnostic criteria closely correlated with clinical features. If neurons appear increased in number in the submucosa the term intestinal neuronal dysplasia (IND) has sometimes been loosely applied without the proposed enzyme histochemistry or quantitation required for the diagnosis of this entity [4]. In the present patient the increase in the submucosal plexus was dramatic. This dramatic increase suggested not IND but diffuse intestinal ganglioneuromatois. In view of this MEN 2B was checked and confirmed by molecular studies. MEN 2B is an autosomal dominant disease caused by an activating missense mutation in the RET proto-oncogene [5]. More than 95 % of the patients have a germline mutation with a methionine to threonine change in codon 918 [6]. The remaining patients show mutations elsewhere in the RET gene e.g. codon 883 [7]. Approximately 50 % of the patients have been shown to have de novo mutations. The disease is associated with 100% penetrance. The phenotype comprises mucosal neuromas, intestinal ganglioneuromatosis, Marfanoid facies, medullary thyroid carcinoma, phaeochromocytoma and parathyroid hyperplasia [8]. MEN 2B is frequently associated with gastrointestinal symptoms, especially constipation, sometimes alternating with diarrhoea. Colonic dysmotility has been reported to be present in up to 90% of the patients, with the symptoms often dating from early infancy [9, 10]. As the disease is associated with a high rate of de novo mutations and many of the phenotypic features may not recognizable for several years, it is important to be familiar with the changes in the alimentary tract if a biopsy is taken early for the investigation of constipation. Once the possibility of this diagnosis has been raised, confirmation is usually easy as 95% of the patients show the Met918Thr mutation. Early diagnosis can be critical for patient management as the risk of medullary carcinoma of the thyroid has been considered to be present in 100% of the patients [11]. This tumour has been reported in patients as young as 7 months [9] or 8 months as in this patient. Metastases can also occur in early childhood [12]. The typical lesions of MEN 2B in the alimentary tract include mucosal neuromas and diffuse intestinal ganglioneuromatosis [13]. These are two very distinct lesions although sometimes they seem to be confused [14, 15]. Mucosal neuromas are composed of numerous tortuous nerves underneath the epithelium with thickened perineurium and increase in mucoid ground substance. Neurons are seldom seen. Although the lesions can be noted at birth in some patients, they may not be obvious until the children are several years old [10]. Ganglioneuromatosis is composed of a marked proliferation of nerve fibres and neurons involving mainly the myenteric plexus. This lesion has been estimated to be present in 90% of patients with MEN 2B [9]. The submucosal plexus may be involved, and also sometimes the mucosa with increase in neurons and nerve fibres in the lamina propria, although the involvement of these more superficial layers is considered to be less consistent and dramatic. There are only a few reports of patients in whom hyperplasia of the submucosal plexus is specifically mentioned [8, 14, 16]. In at least two patients the features were initially considered to be indicative of IND [8, 16]. This entity is still highly controversial due to the lack of user friendly diagnostic criteria and close correlation with clinical features. Whatever one's personal view on IND may be, the suggested assessment is based on enzyme histochemistry using lactic and succinic dehydrogenases [4], and the increase in neurons seem to be subtle as shown by the high rate of discrepancy between closely collaborating pathologists [17]. If the hypertrophy of the submucosal plexus is dramatic, intestinal ganglioneuromatosis must be considered, and the possibility of a genetic disease such as MEN 2B checked. Other genetic conditions which have been reported with diffuse intestinal ganglioneuromatosis include neurofibromatosis type 1 and Cowden syndrome [18]. The hypertrophy of the submucosal plexus can be quite dramatic. As seen in this patient up to 1/3 of the submucosal area is occupied by the nerve fibres and neurons. This change is quite obvious on standard haematoxylin and eosin stained sections. . In view of the identification of the mutation in the RET gene and the absence of the Waardenberg syndrome in the mother and the patient, the family history was considered to be a red herring. Although the changes were obvious in this patient, it is unclear how regularly this feature is sufficiently developed in early infancy to allow a confident diagnosis. Only with a large series can the reliability of this diagnostic feature be assessed. References Kaplan P, de Chaderevian JP. Piebaldism-Waardenburg syndrome: histopathologic evidence for a neural crest syndrome. Am J Med Genet 1988; 31: 679-688. Chow CW, Chan WC, Yue PC. Histochemical criteria for the diagnosis of Hirschsprung's disease in rectal suction biopsies by acetylcholinesterase activity. J Pediatr Surg 1977; 12: 675-80. Southwell BR, King SK, Hutson JM. Chronic constipation in children: organic disorders are a major cause. 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