Endo Paget Monostotic Activity Assessment

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name: endo-paget-monostotic-activity-assessment
description: Assesses biochemical activity in untreated monostotic Paget's disease by measuring P1NP or BSAP and CTx or NTx when scintigraphy shows disease activity despite normal total alkaline phosphatase. Triggered when evaluating disease activity in patients with suspected or confirmed monostotic (single‑site) Paget's disease.
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# Assess activity in monostotic Paget's disease using specific markers

## STEP 1 — Gather Information
Obtain plain radiographs to confirm a monostotic lesion, review serum total ALP if available, and perform a radionuclide bone scan to assess disease activity.  
**Action:** Proceed to measure specific bone turnover markers if total ALP is normal or unavailable.

## STEP 2 — Rule In / Rule Out
Determine whether the bone scan shows focal increased uptake (positive for activity).  
**Action:** If positive, move to marker measurement; if negative, consider disease inactive and forego further marker testing.

## STEP 3 — Classify or Stratify
Measure P1NP or BSAP (formation marker) and CTx or NTx (resorption marker).  
**Action:** If either marker is elevated above the reference range, classify as active disease; if both markers are normal but the bone scan is positive, classify as low‑turnover active disease; if both markers are normal and the bone scan is negative, classify as inactive disease.

## STEP 4 — Decide
For active or low‑turnover active disease, initiate bisphosphonate therapy (e.g., a single 5 mg IV zoledronate) in patients at risk for complications; for inactive disease, reserve treatment and schedule routine clinical follow‑up.  
**Action:** Treat or observe based on classification.

## Clinical Guardrails / Mimics / Pitfalls
Markers can be normal despite scintigraphic activity; do not rely on total ALP alone. Avoid marker testing in severe hepatic impairment (affects ALP‑based assays). Ensure renal function (eGFR > 35 mL/min) before IV zoledronate. Do not withhold therapy based solely on normal markers when the scan is positive.

## Concrete Clinical Example
A 66‑year‑old man with an isolated sclerotic lesion in the right tibia, normal total ALP, and a bone scan showing focal uptake; P1NP is normal, NTx is elevated → classified as active, receives a single 5 mg IV zoledronate dose.

**Source:** Paget’s Disease of Bone: An Endocrine Society Clinical Practice Guideline, Endocrine Society, 2014, doi:10.1210/jc.2014-2910