The clinical features of MEN-IIA depend on the type of tumor present. The pheochromocytomas in MEN-IIA usually produce epinephrine, and increased epinephrine excretion may be the only abnormality early in the course of the disease. Hypertensive crisis secondary to pheochromocytoma is a common presentation, and many of the reported kindreds first come to medical attention after bilateral pheochromocytomas in the proband are diagnosed. Hypertension in patients with pheochromocytoma in MEN-IIA syndrome is more often paroxysmal than sustained, in contrast to the usual sporadic case. The pheochromocytomas are almost always benign, but a tendency for local recurrence has been noted in some of the reported kindreds.
Hyperparathyroidism is less common than medullary carcinoma of the thyroid or pheochromocytoma.
As in the MEN-I syndrome, the hyperparathyroidism frequently involves multiple glands as either diffuse hyperplasia or multiple adenomas. An increased incidence of Hirschsprung's disease, a congenital disorder affecting intestinal motility, has been reported in children of at least one MEN-IIA kindred. Since pheochromocytoma may be asymptomatic in MEN-IIA patients, it may be difficult to exclude pheochromocytoma with certainty. Vanillylmandelic acid excretion is often normal early in the course of disease. CT or MRI is useful in localizing the pheochromocytoma or establishing the presence of bilateral lesions.