## **Core Concept**
Primary idiopathic polymyositis is an inflammatory muscle disease characterized by muscle inflammation and weakness. It is part of a group of diseases known as idiopathic inflammatory myopathies. The condition primarily affects the proximal muscles.

## **Why the Correct Answer is Right**
Polymyositis is known for its involvement of the proximal muscles, skin, and other organs are not typically involved in the initial stages but can be affected in certain subsets of the disease. The condition is characterized by inflammation of the muscles (myositis) without a clear cause (idiopathic).

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because polymyositis does involve muscles.
- **Option B:** This option is incorrect because skin involvement is more characteristic of dermatomyositis, another type of idiopathic inflammatory myopathy, but it does not exclude the possibility of some skin manifestations in certain cases of polymyositis; however, it's not a defining feature.
- **Option C:** This option seems to suggest an absence of muscle involvement which contradicts the definition of polymyositis.
- **Option D:** Given that the question does not specify what each option (A, B, C, D) represents, we infer based on common knowledge about polymyositis.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that polymyositis characteristically spares the muscles of the eyes and the muscles of mastication (chewing), and it does not typically involve the distal muscles initially. Also, remember that the presence of certain autoantibodies can help in diagnosing and classifying these myopathies.

## **Correct Answer:** D. ocular muscles.