Differential Diagnosis for Dry, Scaly, Pruritic Rash on the Trunk and Extremities

Single Most Likely Diagnosis

• A. Zinc deficiency: Zinc deficiency is a well-known cause of skin lesions, including dry, scaly, and pruritic rashes. Patients receiving total parenteral nutrition (TPN) are at risk for zinc deficiency due to inadequate supplementation or increased demand. Zinc plays a crucial role in maintaining skin integrity, and its deficiency can lead to various skin manifestations.

Other Likely Diagnoses

• B. Vitamin A deficiency: Vitamin A is essential for maintaining the integrity of the skin and mucous membranes. Deficiency can cause dry, scaly skin, and patients on TPN may be at risk if they do not receive adequate supplementation.
• D. Free fatty acid deficiency: Essential fatty acid deficiency can occur in patients receiving TPN, especially if the lipid emulsion is not provided or is inadequate. This deficiency can lead to skin symptoms, including dryness and scaling.

Do Not Miss Diagnoses

• C. Vitamin C deficiency: Although less common, vitamin C deficiency (scurvy) can cause skin symptoms, including dryness and poor wound healing. While it might not be the first consideration, missing this diagnosis could lead to significant morbidity, especially in patients with limited mobility or those undergoing surgical procedures.

Rare Diagnoses

• Other nutritional deficiencies (e.g., biotin, niacin) could potentially cause skin rashes but are less likely and more rare compared to the deficiencies listed above. These would be considered in the differential diagnosis if the more common causes are ruled out and the patient's condition does not improve with standard treatments.