**Core Concept**
Lichen planus is a chronic inflammatory and immune-mediated disease that affects the skin, mucous membranes, and other areas of the body. The exact pathogenesis of lichen planus is not fully understood, but it is believed to involve a combination of genetic predisposition, environmental triggers, and an abnormal immune response.

**Why the Correct Answer is Right**
The correct answer for the treatment of choice (TOC) in lichen planus is **D. Systemic corticosteroids with or without immunosuppressive agents**. This treatment approach is often used for severe cases of lichen planus that are resistant to topical corticosteroids. Systemic corticosteroids work by suppressing the immune system and reducing inflammation, while immunosuppressive agents such as cyclosporine or azathioprine can help to modify the abnormal immune response.

**Why Each Wrong Option is Incorrect**
**Option A:** Topical corticosteroids are often used as a first-line treatment for mild to moderate cases of lichen planus, but they may not be effective for severe cases.
**Option B:** Retinoids, such as acitretin, can be used to treat lichen planus, but they are typically reserved for cases that are resistant to other treatments.
**Option C:** Antihistamines are not a primary treatment for lichen planus, as they do not address the underlying immune-mediated inflammation.

**Clinical Pearl / High-Yield Fact**
In cases of severe lichen planus, particularly those involving the oral mucosa, it is essential to evaluate for potential associations with other autoimmune disorders, such as hepatitis C or Sjögren's syndrome.

**Correct Answer:** D. Systemic corticosteroids with or without immunosuppressive agents.