**Core Concept**
In HIV patients with a CD4 count less than 100 cells per microliter, opportunistic infections and malignancies become more prevalent due to immunosuppression. One such condition is the development of pulmonary tuberculosis (TB), which can present with a non-productive cough.

**Why the Correct Answer is Right**
The correct answer is related to the diagnosis of pulmonary TB in an immunocompromised patient. TB is caused by Mycobacterium tuberculosis, which primarily infects cells of the monocyte/macrophage lineage. In HIV patients with a CD4 count less than 100 cells per microliter, the immune system is severely compromised, increasing the risk of reactivation of latent TB. The presentation of TB in these patients often includes a non-productive cough, which is a common symptom of pulmonary TB.

**Why Each Wrong Option is Incorrect**

* **Option A:** Pneumocystis jirovecii pneumonia (PCP) is a common opportunistic infection in HIV patients with a CD4 count less than 100 cells per microliter, presenting with a non-productive cough, but it is not the correct answer as the question is asking for an option that is "not seen".
* **Option B:** Lymphoma is a type of malignancy that can occur in HIV patients, but it is not typically associated with a non-productive cough as a primary symptom.
* **Option C:** Cytomegalovirus (CMV) pneumonia is another opportunistic infection that can occur in HIV patients with a CD4 count less than 100 cells per microliter, but it typically presents with a productive cough and is not the correct answer.

**Clinical Pearl / High-Yield Fact**
In HIV patients with a CD4 count less than 100 cells per microliter, a non-productive cough can be a presenting symptom of pulmonary TB. It is essential to consider TB in the differential diagnosis of a non-productive cough in these patients, along with other opportunistic infections and malignancies.

**Correct Answer:** B. Lymphoma