**Core Concept**
L.D. bodies, also known as Levodopa-Dopa bodies, are intracellular inclusions found in the neurons of patients with neurodegenerative diseases. They are composed of a complex of alpha-synuclein protein and ubiquitin. The presence of L.D. bodies is a hallmark of certain neurodegenerative disorders.

**Why the Correct Answer is Right**
L.D. bodies are specifically associated with Lewy body dementia, Parkinson's disease, and multiple system atrophy. They are formed due to the accumulation of alpha-synuclein protein in the neurons, which is a result of impaired protein degradation and aggregation. This process leads to the formation of insoluble fibrils that accumulate in the cytoplasm of neurons, forming L.D. bodies.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because L.D. bodies are not typically associated with Alzheimer's disease, although both diseases are neurodegenerative disorders. Alzheimer's disease is characterized by the accumulation of amyloid-beta plaques and tau protein tangles.
**Option B:** This option is incorrect because Huntington's disease is characterized by the expansion of a CAG repeat in the Huntingtin gene, leading to the formation of huntingtin protein inclusions, not L.D. bodies.
**Option C:** This option is incorrect because Amyotrophic Lateral Sclerosis (ALS) is characterized by the accumulation of TDP-43 protein inclusions, not L.D. bodies.

**Clinical Pearl / High-Yield Fact**
L.D. bodies are a key feature of Lewy body dementia and Parkinson's disease, and their presence can be used to diagnose these conditions. However, it's essential to note that the presence of L.D. bodies alone is not sufficient for diagnosis, as other neurodegenerative diseases can also exhibit similar inclusions.

**Correct Answer: D. Multiple system atrophy**