Atopic Dermatitis (Eczema): This condition is characterized by itchy, inflamed skin that can appear anywhere on the body, including the elbow folds, abdomen, and face. The sudden onset and presence of plaque-like areas are consistent with an eczematous reaction, which could be triggered by various factors including allergens or irritants, even if the patient denies changing anything.

Contact Dermatitis: This is a type of inflammation of the skin that occurs when the skin comes into contact with an irritant or allergen. Given the locations (elbow folds, abdomen, and face), it's possible that the patient came into contact with something that triggered this reaction, even if they're not aware of it.
Seborrheic Dermatitis: This condition causes scaly patches, red skin, and stubborn dandruff due to an oily scalp. It can also appear on oily areas of the body, such as the face, and could potentially cause itchy plaque-like areas, although it's less common in the elbow folds and abdomen.
Psoriasis: An autoimmune condition that speeds up the life cycle of skin cells, causing cells to build up rapidly on the surface of the skin. The extra skin cells form scales and red patches that itch or burn. While the sudden onset is less typical for psoriasis, it cannot be ruled out without further examination.

Bullous Pemphigoid: An autoimmune disease that causes blistering of the skin. Although it typically presents with blisters rather than plaque-like areas, it's crucial to consider due to its potential severity and the need for prompt treatment.
Dermatitis Herpetiformis: A skin manifestation of celiac disease, characterized by intensely itchy blisters. It's essential to consider this diagnosis due to its association with an underlying condition (celiac disease) that requires specific management.
Erythema Multiforme: A skin condition characterized by target lesions, which can sometimes appear as itchy plaques. It can be triggered by infections or medications and has a range of severity, making it a critical diagnosis not to miss.

Pityriasis Rubra Pilaris (PRP): A rare skin disorder that causes constant itching and scaling (exfoliation) of the skin. While it's less likely given the sudden onset and specific locations, it's a diagnosis to consider in the differential due to its distinct presentation.
Granuloma Annulare: A benign skin condition characterized by small, circular bumps that are often localized to the forearms, hands, or feet but can appear elsewhere. It's less common on the face and abdomen but could be considered in a broad differential diagnosis.