**Question:** Koenen's periungal fibroma is seen in –

A. Ehlers-Danlos syndrome
B. Proteus syndrome
C. Marfan syndrome
D. Turner syndrome

**Core Concept:** Koenen's periungal fibroma is a clinical sign representing a hyperproliferation disorder of cutaneous fibroblasts. It is characterized by benign, painless, and asymptomatic fibromatous nodules found in the periungual region, mainly affecting the fingers and toes.

**Why the Correct Answer is Right:**

Koenen's periungal fibroma is primarily associated with Ehlers-Danlos syndrome (EDS), a group of genetic connective tissue disorders characterized by loose skin, joint hypermobility, and fragility. In EDS, fibroblasts over-produce collagen, leading to the formation of fibromatous nodules in the periungual region.

**Why Each Wrong Option is Incorrect:**

- Proteus syndrome (B): Proteus syndrome is a rare genetic disorder characterized by unequal growth of parts of the body. Koenen's periungal fibroma is not a feature of Proteus syndrome.

- Marfan syndrome (C): Marfan syndrome is a connective tissue disorder affecting the skin, bones, and cardiovascular system. Koenen's periungal fibroma is not a typical feature of Marfan syndrome.

- Turner syndrome (D): Turner syndrome is a genetic disorder in females resulting from the absence of one X chromosome. Koenen's periungal fibroma is not a feature of Turner syndrome.

**Clinical Pearl:**

Koenen's periungual fibroma is a clinical sign that helps differentiate these disorders from each other. This differential diagnosis is crucial in guiding appropriate treatment and management strategies. For example, if a patient presents with periungual fibromatosis, the presence of Koenen's sign may suggest Ehlers-Danlos syndrome, guiding the clinician to evaluate for underlying connective tissue disorders and manage the patient accordingly.