Differential Diagnosis

The patient presents with brownish, non-itchy spots under the right breast. Considering the history and physical examination, the following differential diagnoses are proposed:

• Single Most Likely Diagnosis
  • Contact Dermatitis: Given the location under the breast, which is a common area for friction and moisture accumulation, and the fact that a similar issue resolved with a gel in the past, contact dermatitis is a plausible diagnosis. The lack of itchiness does not rule out this condition, as not all forms of contact dermatitis are pruritic.
• Other Likely Diagnoses
  • Intertrigo: This is a type of skin inflammation caused by skin-on-skin friction, typically occurring in warm, moist areas of the body, such as under the breasts. It can present with brownish discoloration and is consistent with the location of the spots.
  • Seborrheic Keratosis: These are benign growths that can appear as brownish spots. Their presence in a new location could explain the patient's symptoms, although they are typically more raised and verrucous.
  • Eczema (Atopic Dermatitis): Although the patient reports the spots are not itchy, some forms of eczema can present without significant pruritus, especially in adults. The history of a similar issue in a different location that resolved with a gel (potentially a topical steroid) supports this consideration.
• Do Not Miss Diagnoses
  • Breast Cancer: Although rare, any new skin changes under the breast should prompt consideration of breast cancer, particularly if there's an associated mass or other symptoms. Inflammatory breast cancer can present with skin changes, including discoloration, without a distinct lump.
  • Paget's Disease of the Breast: This rare form of breast cancer can present with eczematous changes of the nipple and areola, which could potentially extend under the breast. It's crucial to rule out this condition due to its implications for breast health.
• Rare Diagnoses
  • Mastocytosis: A condition characterized by the accumulation of mast cells in the skin, which can lead to brownish lesions. It's less likely given the localized nature of the patient's symptoms but should be considered if other diagnoses are ruled out.
  • Nevus of Ota: A benign condition characterized by hyperpigmentation, typically around the eye, but can occur in other areas. It's less common under the breast but could be considered if the spots are pigmented and not changing.

Each diagnosis should be evaluated based on a thorough history, physical examination, and potentially diagnostic tests such as biopsies for suspicious lesions or further imaging if breast cancer is a concern.