Differential Diagnosis for Patient with SLE and Black Scaly Lips and Rash

Single Most Likely Diagnosis

• SLE Exacerbation: Given the patient's history of Systemic Lupus Erythematosus (SLE), an exacerbation of the disease is the most likely cause of the new symptoms. SLE can cause a wide range of skin manifestations, including rashes and mucosal lesions. The black scaly lips could be indicative of a lupus-related mucosal lesion or possibly discoid lupus, which is a form of cutaneous lupus that can cause scaly, disc-shaped lesions.

Other Likely Diagnoses

• Discoid Lupus Erythematosus (DLE): This is a chronic skin condition characterized by inflammation and scarring type lesions, often on the face, ears, and scalp, but can also occur on the lips and back. It is closely associated with SLE but can occur independently.
• Photosensitive Rash: Many patients with SLE are sensitive to sunlight, which can trigger or exacerbate skin rashes. The rash on the back could be a photosensitive reaction, especially if the patient has been exposed to sunlight recently.
• Cutaneous Vasculitis: This condition involves inflammation of the blood vessels in the skin and can be associated with SLE. It can cause a variety of skin lesions, including rashes and ulcers.

Do Not Miss Diagnoses

• Infections (e.g., bacterial, fungal, viral): Patients with SLE are often on immunosuppressive therapy, making them more susceptible to infections. Certain infections can cause skin manifestations similar to those described, and missing an infection could lead to severe consequences.
• Malignancy (e.g., skin cancer): Although less common, skin cancers or other malignancies could present with skin lesions. Given the patient's immunosuppressed state, the risk might be higher, and missing a malignancy could be catastrophic.

Rare Diagnoses

• Pellagra: A condition caused by niacin deficiency, characterized by dermatitis, diarrhea, dementia, and potentially death if left untreated. The dermatitis can be similar to a photosensitive rash and could be considered in patients with malabsorption or poor dietary intake, which might be more common in those with chronic diseases like SLE.
• Sjögren's Syndrome: An autoimmune disorder that can cause skin manifestations, including rashes, and is often associated with other autoimmune diseases like SLE. However, its primary symptoms involve exocrine glands, particularly the salivary and lacrimal glands, leading to dry mouth and eyes.

Each of these diagnoses should be considered and evaluated based on the patient's full clinical presentation, medical history, and laboratory findings to determine the most appropriate treatment plan.