**Core Concept**
Hansen's disease, also known as leprosy, is a chronic bacterial infection caused by *Mycobacterium leprae*. It primarily affects the peripheral nerves, skin, and mucous membranes, leading to a range of symptoms including numbness, weakness, and discoloration. The disease progresses in various stages, with the early stage characterized by the loss of sensation.

**Why the Correct Answer is Right**
In Hansen's disease, the earliest sensation to be lost is the light touch sensation. This occurs due to the involvement of the small nerve fibers, which are responsible for transmitting light touch and pain sensations. The small nerve fibers are the first to be affected by the *M. leprae* bacilli, leading to a loss of light touch sensation in the affected areas. This is often followed by the loss of temperature and pain sensation.

**Why Each Wrong Option is Incorrect**
* **Option A:** Temperature sensation is typically lost later in the disease process, after the loss of light touch and pain sensation.
* **Option B:** Pain sensation is also lost in Hansen's disease, but it occurs after the loss of light touch sensation.
* **Option C:** Motor function is not the earliest sensation to be lost in Hansen's disease, although it may be affected later in the disease process.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that Hansen's disease can present with a wide range of symptoms, and the loss of sensation is often the earliest and most common symptom. The loss of light touch sensation is a key clinical finding that should prompt further investigation for Hansen's disease.

**Correct Answer:** D.