**Core Concept**
The patient's presentation suggests a complex syndrome involving multiple systems, including gastrointestinal, neurological, and endocrine. The combination of chronic constipation, marfanoid habitus, and specific physical findings like neuromas of the tongue and medullated corneal nerve fibers points towards a genetic disorder.

**Why the Correct Answer is Right**
Given the symptoms and signs, particularly the presence of a thyroid nodule, marfanoid habitus, and other specific findings like neuromas and medullated corneal nerve fibers, the patient likely suffers from **Multiple Endocrine Neoplasia (MEN) type 2B**. This rare disorder is characterized by the presence of medullary thyroid carcinoma, pheochromocytoma, and other physical features such as marfanoid habitus and mucosal neuromas.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not align with the specific constellation of symptoms and signs presented, particularly the neuromas and medullated corneal nerve fibers.
**Option B:** Similarly, this option does not fit with the overall clinical picture, especially the presence of a thyroid nodule and the patient's habitus.
**Option C:** This option is also incorrect as it does not account for the full spectrum of the patient's symptoms and physical findings.

**Clinical Pearl / High-Yield Fact**
MEN 2B is distinguished from other forms of MEN by its early onset and the presence of mucosal neuromas and a marfanoid body habitus without other signs of MEN 2A such as hyperparathyroidism. Recognizing the combination of these features is crucial for early diagnosis and management.

**Correct Answer:** D. Multiple Endocrine Neoplasia (MEN) type 2B.