Differential Diagnosis for Elevated Alkaline Phosphatase with Normal AST and ALT

Given the clinical presentation of a 62-year-old woman with a history of cerebrovascular accident (CVA), current smoker, and elevated alkaline phosphatase (ALP) levels with normal aspartate aminotransferase (AST) and alanine aminotransferase (ALT) liver function tests, the following differential diagnoses are considered:

• Single Most Likely Diagnosis
  • Bone-related disorders (e.g., osteomalacia, Paget's disease, bone metastasis): Elevated ALP can be indicative of bone disorders, especially in the context of normal liver enzymes. The patient's age and smoking history increase the risk for bone-related conditions.
• Other Likely Diagnoses
  • Vitamin D deficiency: Common in older adults, especially those with limited sun exposure or inadequate dietary intake. Vitamin D deficiency can lead to elevated ALP.
  • Primary hyperparathyroidism: Can cause elevated ALP due to increased bone turnover.
  • Chronic kidney disease: May lead to elevated ALP due to secondary hyperparathyroidism.
• Do Not Miss Diagnoses
  • Biliary obstruction or cholestasis: Although AST and ALT are normal, biliary obstruction can cause isolated elevation of ALP. This condition requires prompt diagnosis and treatment to prevent liver damage.
  • Hepatocellular carcinoma: Rarely, liver cancer can present with isolated ALP elevation. Given the patient's smoking history, which increases the risk of various cancers, this diagnosis should not be overlooked.
• Rare Diagnoses
  • Wilson's disease: A genetic disorder leading to copper accumulation in the liver, which can cause liver dysfunction and elevated ALP. However, it typically presents at a younger age.
  • Sarcoidosis: A systemic granulomatous disease that can affect the liver and bones, leading to elevated ALP. It is less common but should be considered in the differential diagnosis, especially if other systemic symptoms are present.

Each of these diagnoses has a different set of implications for management and prognosis, highlighting the importance of a thorough diagnostic workup to determine the underlying cause of the elevated ALP in this patient.