Differential Diagnosis for 63-year-old Male with Itchy Chest, Underarms, and Respiratory Symptoms
Single Most Likely Diagnosis
- Dermatophytid reaction or allergic contact dermatitis: Given the patient's symptoms of itchy chest, underarms, and small red bumps, along with a head cold, cough, and low-grade fever, a dermatophytid reaction or allergic contact dermatitis could be the primary diagnosis. The presence of a head cold could suggest an allergic reaction, and the skin symptoms are consistent with a dermatological condition.
Other Likely Diagnoses
- Scabies: This parasitic infection is common in crowded areas and can cause intense itching, especially in the underarm area, and small red bumps. The patient's sexual history as a gay male on PrEP (Pre-Exposure Prophylaxis for HIV) increases the risk of sexually transmitted infections, including scabies.
- Folliculitis: An inflammation of the hair follicles, often caused by bacterial or fungal infections, which could explain the itchy, bumpy rash, particularly in areas like the underarms.
- Eczema (atopic dermatitis): A chronic condition characterized by itchy, inflamed skin, which could be exacerbated by the patient's cold and cough, leading to the observed symptoms.
Do Not Miss Diagnoses
- HIV-related rash: Although the patient is on PrEP, the possibility of HIV infection cannot be entirely ruled out, especially if adherence to PrEP has been inconsistent. Certain rashes can be indicative of acute HIV infection.
- Syphilis: A sexually transmitted infection that can cause a variety of skin rashes and symptoms, including those described. Given the patient's sexual history, syphilis is a critical diagnosis not to miss.
- Lymphoma or other malignancies: In rare cases, skin symptoms can be the initial presentation of an underlying malignancy, such as lymphoma. Although less likely, this diagnosis is critical due to its potential severity.
Rare Diagnoses
- Pityriasis rosea: A skin condition characterized by a rash that can appear after a viral infection, which might explain the patient's symptoms following a head cold.
- Keratosis pilaris: A condition that causes small, rough patches on the skin, often on the arms, legs, and buttocks, but less commonly in the underarms or chest, which could potentially cause some of the symptoms described.