Differential Diagnosis
- Single most likely diagnosis
- Pellagra: This condition is caused by a deficiency in niacin (vitamin B3) and is characterized by the "4 Ds": diarrhea, dermatitis, dementia, and potentially death. The darkening of the skin, particularly in areas exposed to sunlight or trauma, along with gastrointestinal symptoms and mucous membrane changes like ulcers in the mouth, fits the presentation of pellagra. The lack of consumption of vegetables, fruits, and potentially other whole foods could lead to this deficiency.
- Other Likely diagnoses
- Scurvy: Caused by a lack of vitamin C, scurvy can lead to skin changes, malaise, and mucous membrane issues, including ulcers. However, the classic presentation includes joint pain and bleeding gums, which are not mentioned here.
- Kwashiorkor: A form of malnutrition that occurs when there is not enough protein in the diet. It can cause skin changes, including darkening, and edema, but typically presents with more pronounced muscle wasting and edema.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Vitamin B12 deficiency: While less directly linked to skin darkening, a severe deficiency can cause neurological issues, gastrointestinal symptoms, and mucocutaneous changes. It's crucial to consider due to the potential for irreversible neurological damage if left untreated.
- Cancer: Certain types of cancer, particularly those affecting the gastrointestinal tract or causing malabsorption, could lead to similar symptoms. The presence of unexplained weight loss, persistent nausea, and diarrhea should prompt an investigation into possible malignancy.
- Rare diagnoses
- Carotenemia: A harmless condition caused by excessive consumption of carotenoid-containing foods (like carrots), leading to a yellow-orange discoloration of the skin. However, given the patient's avoidance of vegetables and fruits, this is highly unlikely.
- Porphyria cutanea tarda: A disorder that can cause blistering skin lesions upon sun exposure and can lead to changes in skin pigmentation. It's less likely given the gastrointestinal and mucous membrane symptoms described.