Differential Diagnosis for Darkened Skin on Lower Back with Pain upon Water Exposure
- Single most likely diagnosis:
- Contact Dermatitis: This condition is characterized by skin inflammation and irritation due to contact with an allergen or irritant. The darkened skin could be a result of post-inflammatory hyperpigmentation, and water might exacerbate the irritation, causing pain.
- Other Likely diagnoses:
- Eczema (Atopic Dermatitis): Similar to contact dermatitis, eczema can cause skin darkening and irritation. Water, especially hot water, can strip the skin of its natural oils, leading to increased dryness and pain.
- Psoriasis: This chronic skin condition can cause dark, scaly patches. While not typically painful with water exposure, the scales can become irritated and painful if scratched or if the skin is further irritated by certain soaps or shampoos used with water.
- Tinea Versicolor: A fungal infection that can cause changes in skin pigmentation, leading to darkened areas. It might not directly cause pain with water exposure, but the condition can lead to itching and irritation.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.):
- Malignancy (e.g., Melanoma): Although less likely, any new or changing skin lesion, especially one that is painful or changes color, should be evaluated for the possibility of skin cancer. Early detection is crucial for treatment and survival.
- Infectious Processes (e.g., Cellulitis, Abscess): Bacterial infections of the skin can cause pain, redness, and swelling. While water exposure might not directly cause pain, the infection could be exacerbated by moisture, leading to increased discomfort.
- Rare diagnoses:
- Aquagenic Pruritus: A rare condition characterized by intense itching without a rash after contact with water. It's less likely to cause darkened skin but could be considered if the primary complaint is pain or itching after water exposure.
- Erythema Dyschromicum Perstans: A rare skin condition that causes progressive, asymptomatic hyperpigmentation. It might not directly relate to pain with water exposure but could be a differential for the darkened skin aspect of the presentation.