**Question:** A 42-year-old man with a small-bowel fistula has been receiving TPN with standard hypertonic glucose-amino acid solution for the previous 3 weeks. The patient is noticed to have scaly, hyperpigmented lesions over the acral surfaces of elbows and knees, similar to enterohepatic acrodermatitis. What is the most likely cause of this condition? SELECT ONE.

A. Hypothyroidism
B. Hypokalemia
C. Acromegaly
D. Diabetes mellitus

**Correct Answer:** D. Diabetes mellitus

**Core Concept:** Enterohepatic acrodermatitis is a clinical condition characterized by hyperpigmented, hyperkeratotic lesions involving the acral surfaces of the extremities, typically seen in patients with diabetes mellitus. The condition is caused by the accumulation of toxic substances derived from the degradation of glucose, amino acids, and electrolytes in the TPN solution, which can lead to skin changes due to hyperglycemia and hyperaminoacidemia.

**Why the Correct Answer is Right:** Diabetes mellitus is the most likely cause of enterohepatic acrodermatitis in this scenario because the patient has been receiving TPN for a prolonged duration, leading to hyperglycemia and hyperaminoacidemia. These conditions cause the accumulation of toxic substances derived from glucose and amino acids in the TPN solution, which can lead to skin changes. The patient's history of having a small-bowel fistula indicates prolonged parenteral nutrition, which is a common risk factor for developing enterohepatic acrodermatitis.

**Why Each Wrong Option is Incorrect:**

A. Hypothyroidism (Hypothyroidism) can cause skin changes as well, but the clinical presentation of enterohepatic acrodermatitis is distinct from hypothyroidism-related skin changes, which are more likely to involve the hands and feet. The correct answer, diabetes mellitus, shares similar skin changes but is related to the accumulation of toxic substances derived from glucose and amino acids in the TPN solution.

B. Hypokalemia (Low potassium levels) is unlikely to cause the described skin changes, as the condition usually presents with muscle weakness, tetany, and cardiac arrhythmias, not hyperkeratotic and hyperpigmented lesions.

C. Acromegaly (Excess growth hormone production) can lead to acromegaly-related skin changes, but these are distinct from the described skin changes of enterohepatic acrodermatitis.

D. Hyperglycemia (High blood sugar levels) from diabetes mellitus is the most likely cause of the described skin changes, as it leads to the accumulation of toxic substances derived from glucose in the TPN solution. This can cause hyperkeratotic and hyperpigmented lesions, similar to those described in the question.

**Clinical Pearls:**

1. Enterohepatic acrodermatitis is a clinical entity seen in patients on prolonged TPN therapy due to the accumulation of toxic substances derived from glucose and amino acids in the TPN solution.
2. The presence of hyperker