## Core Concept
Nasal myiasis refers to the infestation of the nasal cavity by larvae of flies, typically seen in neglected or immunocompromised individuals. The condition is often associated with poor hygiene and exposure to unsanitary environments. The presenting symptoms are usually related to the local irritation and tissue damage caused by the larvae.

## Why the Correct Answer is Right
The correct answer, **nasal discharge**, is a direct consequence of the infestation. The larvae feed on the nasal mucosa and surrounding tissues, leading to necrosis and a significant inflammatory response. This results in a purulent and often foul-smelling nasal discharge, which is a hallmark of nasal myiasis. The discharge may be bloody or contain fragments of tissue and live larvae.

## Why Each Wrong Option is Incorrect
- **Option A:** While pain or discomfort could be a symptom, it is not the most specific or commonly emphasized presenting feature of nasal myiasis.
- **Option B:** Although nasal obstruction could occur due to swelling and the presence of larvae, it is not the primary or most characteristic symptom.
- **Option C:** This option seems to relate to another condition or is not directly relevant to the typical presentation of nasal myiasis.

## Clinical Pearl / High-Yield Fact
A key point to remember is that nasal myiasis has a strong association with poor socioeconomic conditions and is often seen in patients with a compromised immune system or those with a history of trauma or surgery in the nasal area. A classic presentation includes a patient with a history of recent travel to or residence in an area with poor sanitation, presenting with foul-smelling nasal discharge.

**Correct Answer: D. nasal discharge**