Okay, let's tackle this question. The patient is a 56-year-old man with a history of Non-Hodgkin's lymphoma treated with chemotherapy a year ago. He now has a painful rash on his right upper eyelid and forehead for 48 hours. Vital signs are normal except maybe the temperature, which is 98°F, so not elevated. The question is asking for the most likely diagnosis.

First, I need to think about possible causes of a painful rash in someone with a history of chemotherapy. Chemotherapy can suppress the immune system, making the patient more susceptible to infections. Also, the location of the rash on the eyelid and forehead is important. The trigeminal nerve has three branches, and the ophthalmic branch (V1) innervates the forehead and eyelid.

Herpes zoster ophthalmicus comes to mind because it's caused by reactivation of VZV in the ophthalmic division. The rash is typically unilateral, painful, and in the V1 distribution. Since the patient had chemotherapy, his immune system might be compromised, leading to reactivation of latent VZV. The absence of fever might be because the immune system is already compromised, so he doesn't mount a typical fever response.

Now, let's consider other options. Shingles is a classic possibility. But are there other possibilities? Maybe contact dermatitis? But that's usually itchy rather than painful. Cellulitis could be a concern, but the localized nature and the history of immunosuppression point more towards a viral infection.

The correct answer is likely herpes zoster ophthalmicus. The key points here are the distribution of the rash (V1), the history of immunosuppression from chemotherapy, and the presence of pain. The other options don't fit as well. For example, impetigo is bacterial and more common in children, and the rash would be different. Eczema herpeticum is another possibility, but that's more widespread and also in eczema-prone areas.

So, the answer should be herpes zoster ophthalmicus. The other options like impetigo, eczema herpeticum, or contact dermatitis don't fit the clinical picture as well. The key here is the dermatomal distribution and the immunosuppressed state.

**Core Concept**
The question tests knowledge of herpes zoster ophthalmicus (HZO), a reactivation of varicella-zoster virus (VZV) in the ophthalmic division of the trigeminal nerve. Chemotherapy-induced immunosuppression increases susceptibility to VZV reactivation, and HZO presents with unilateral **painful** rashes in the **V1 dermatome** (forehead, eyelid, and sometimes the tip of the nose).

**Why the Correct Answer is Right**
Herpes zoster ophthalmicus occurs due to VZV reactivation in the ophthalmic branch (V1) of the trigeminal nerve. The patient’s history of chemotherapy (immunosuppression) and the unilateral, painful rash on the right upper eyelid/forehead (V1 distribution) are classic. Pain is a hallmark of HZO, often preceding the rash. Unlike other rashes, HZO spares the glabella (midline) due to the **Hutchinson sign**, but this

✓ Correct Answer: B. Herpes zoster