What is the most appropriate initial test to confirm the diagnosis of a patient with hip pain at night that is relieved with walking, suggesting a possible bone pathology such as Paget's disease?

Alkaline Phosphatase is the Confirmatory Test

For hip pain at night relieved with walking—a classic presentation of Paget's disease of bone—alkaline phosphatase is the most appropriate laboratory test to confirm the diagnosis. 1

Clinical Reasoning

The clinical presentation described is pathognomonic for Paget's disease of bone:

• Night pain relieved by walking is characteristic of the increased bone turnover and vascular congestion seen in active Paget's disease 2
• This pattern distinguishes it from mechanical hip pathology (worse with activity) or inflammatory arthritis (morning stiffness) 1

Why Alkaline Phosphatase

Elevated serum alkaline phosphatase directly correlates with disease activity in Paget's disease and is the primary biochemical marker for diagnosis. 1

• Alkaline phosphatase reflects the accelerated osteoblastic activity that follows the initial osteoclastic bone resorption in Paget's disease 1
• The degree of elevation corresponds to the extent and activity of the disease 1
• This test is widely available, inexpensive, and highly sensitive for active disease 3

Why Not the Other Tests

• Phosphorus: Normal in Paget's disease; does not reflect bone turnover activity 1
• Calciferol (Vitamin D): Not diagnostically useful for Paget's disease; may be low in many elderly patients regardless of Paget's disease 1
• GGT (Gamma-glutamyl transferase): A liver enzyme unrelated to bone pathology 1
• Creatine phosphokinase: Reflects muscle damage, not bone remodeling; normal in Paget's disease 1

Diagnostic Algorithm After Alkaline Phosphatase

Once elevated alkaline phosphatase is confirmed:

1. Obtain plain radiographs of the symptomatic hip to identify characteristic findings (cortical thickening, coarsened trabeculae, bone expansion) 1, 3
2. Nuclear bone scintigraphy is the most sensitive test to identify all sites of involvement and confirm the diagnosis 1
3. Consider liver function tests to exclude hepatic causes of elevated alkaline phosphatase if the clinical picture is unclear 3

Critical Pitfall to Avoid

Do not delay imaging if alkaline phosphatase is elevated—radiographic confirmation is essential as alkaline phosphatase can be elevated in other conditions (liver disease, other bone disorders). The combination of elevated alkaline phosphatase plus characteristic radiographic findings confirms Paget's disease. 1, 3