**Core Concept**
Alopecia universalis is a rare autoimmune disease characterized by the loss of all body hair, including scalp hair, eyebrows, eyelashes, and pubic hair. It is a variant of alopecia areata, a condition where the immune system attacks the hair follicles, leading to patchy hair loss.

**Why the Correct Answer is Right**
Alopecia universalis is caused by a cell-mediated immune response against the hair follicles, resulting in the destruction of hair-producing cells. This leads to a complete loss of body hair, including scalp hair, eyebrows, eyelashes, and pubic hair. The condition is often associated with other autoimmune diseases, such as thyroid disease and vitiligo. The hair loss in alopecia universalis is usually irreversible and can be frustrating for patients.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because alopecia universalis is not limited to scalp hair loss; it affects all body hair.
**Option C:** This option is incorrect because hair loss in alopecia universalis is not limited to the scalp margin; it affects all areas of the body.
**Option D:** This option is incorrect because male pattern hair loss, also known as androgenetic alopecia, is a different condition characterized by hair thinning and loss, particularly on the scalp, due to the effects of dihydrotestosterone (DHT) on hair follicles.

**Clinical Pearl / High-Yield Fact**
Alopecia universalis is often associated with other autoimmune diseases, such as thyroid disease, vitiligo, and pernicious anemia, and patients may require a comprehensive evaluation to rule out these conditions.

**✓ Correct Answer: B. Loss of all body hair**