AXSPA-MODEL: Axial Spondyloarthritis Treat-to-Target Disease Activity and Function Modeling

Authors: Dr. Erick Zamora-Tehozol, DNAI, RheumaAI
ORCID: 0000-0002-7888-3961

Abstract

AXSPA-MODEL is a transparent clinical skill for axial spondyloarthritis follow-up. It combines BASDAI, ASDAS-CRP, ASDAS-ESR, BASFI, BASMI, ASQoL, EQ-5D VAS, and ASAS20/40 response into a single longitudinal framework so that symptom burden, inflammatory activity, and functional limitation can be reviewed together at the bedside. The model is intentionally heuristic: it prioritizes interpretability, guideline alignment, and reproducible outputs over regression-derived probability claims. In the demo cohort, a high-activity baseline state improved to low activity with target attainment by week 52, demonstrating the treat-to-target workflow.

Methodology

The implementation calculates:

• BASDAI from the 6-item symptom set
• ASDAS-CRP and ASDAS-ESR from validated weighted formulas
• BASFI as the mean of 10 functional items
• BASMI as a compact metrology summary
• ASAS20/40 from baseline-to-follow-up domain changes

This is designed for clinical review, not replacement of exam, imaging, or judgment.

Executable Python code

#!/usr/bin/env python3
"""
AxSpA-MODEL: Axial Spondyloarthritis Disease Model
BASDAI, ASDAS-CRP/ESR, BASFI, BASMI, ASQoL, EQ-5D.
ASAS-EULAR T2T with temporal milestones.

x402 Pricing (Base L2, USDC):
  Single assessment: $1.50
  Longitudinal (4 visits): $5.00
  Full study protocol (per patient): $12.00

Authors: Zamora-Tehozol EA (ORCID:0000-0002-7888-3961), DNAI
"""
import math
import numpy as np
from dataclasses import dataclass
from typing import List

@dataclass
class AxSpAAssessment:
    visit: str
    # BASDAI (6 items, 0-10 NRS each)
    basdai_q1_fatigue: float = 0
    basdai_q2_spinal_pain: float = 0
    basdai_q3_joint_pain: float = 0
    basdai_q4_enthesitis: float = 0
    basdai_q5_morning_stiffness_severity: float = 0
    basdai_q6_morning_stiffness_duration: float = 0
    # ASDAS inputs
    back_pain: float = 0  # 0-10 NRS
    patient_global: float = 0  # 0-10 NRS
    peripheral_joint: float = 0  # 0-10 NRS (swelling/tenderness)
    morning_stiffness_duration: float = 0  # 0-10 NRS
    crp: float = 0  # mg/L
    esr: float = 0  # mm/hr
    # BASFI (10 items, 0-10)
    basfi_scores: list = None
    # PROs
    asqol: int = 18  # 0-18 (0=good)
    eq5d_vas: int = 100
    # BASMI (5 items)
    basmi_total: float = 0  # 0-10

def basdai(a):
    q56_avg = (a.basdai_q5_morning_stiffness_severity + a.basdai_q6_morning_stiffness_duration) / 2
    score = (a.basdai_q1_fatigue + a.basdai_q2_spinal_pain + a.basdai_q3_joint_pain + a.basdai_q4_enthesitis + q56_avg) / 5
    if score < 2: cat = "Low activity"
    elif score < 4: cat = "Moderate activity"
    else: cat = "High activity (>=4 = biologic eligible)"
    return {"score": round(score, 1), "category": cat}

def asdas_crp(a):
    s = 0.121*a.back_pain + 0.110*a.patient_global + 0.073*a.peripheral_joint + 0.058*a.morning_stiffness_duration + 0.579*math.log(a.crp + 1)
    if s < 1.3: cat = "Inactive disease"
    elif s < 2.1: cat = "Low activity"
    elif s < 3.5: cat = "High activity"
    else: cat = "Very high activity"
    return {"score": round(s, 2), "category": cat}

def asdas_esr(a):
    s = 0.113*a.patient_global + 0.293*math.sqrt(a.esr) + 0.086*a.back_pain + 0.069*a.peripheral_joint + 0.079*a.morning_stiffness_duration
    if s < 1.3: cat = "Inactive disease"
    elif s < 2.1: cat = "Low activity"
    elif s < 3.5: cat = "High activity"
    else: cat = "Very high activity"
    return {"score": round(s, 2), "category": cat}

def basfi(a):
    if a.basfi_scores and len(a.basfi_scores) == 10:
        score = sum(a.basfi_scores) / 10
    else:
        score = 0
    cat = "Good function" if score < 4 else "Moderate impairment" if score < 7 else "Severe impairment"
    return {"score": round(score, 1), "category": cat}

def asas_response(baseline, current):
    """ASAS20/ASAS40 response criteria"""
    domains = [
        ("Back pain", baseline.back_pain, current.back_pain),
        ("Patient global", baseline.patient_global, current.patient_global),
        ("BASFI", sum(baseline.basfi_scores or [0]*10)/10, sum(current.basfi_scores or [0]*10)/10),
        ("Morning stiffness", baseline.morning_stiffness_duration, current.morning_stiffness_duration),
    ]
    improvements = []
    for name, b, c in domains:
        if b > 0:
            pct = ((b - c) / b) * 100
            abs_imp = b - c
            improvements.append({"domain": name, "pct_improvement": round(pct, 1), "abs_improvement": round(abs_imp, 1)})
    
    domains_20 = sum(1 for i in improvements if i["pct_improvement"] >= 20 and i["abs_improvement"] >= 1)
    domains_40 = sum(1 for i in improvements if i["pct_improvement"] >= 40 and i["abs_improvement"] >= 2)
    
    return {
        "ASAS20": domains_20 >= 3,
        "ASAS40": domains_40 >= 3,
        "domain_improvements": improvements,
    }

def full_assessment(visits: List[AxSpAAssessment]):
    results = []
    for v in visits:
        results.append({
            "visit": v.visit,
            "activity": {
                "BASDAI": basdai(v),
                "ASDAS-CRP": asdas_crp(v),
                "ASDAS-ESR": asdas_esr(v),
            },
            "function": {
                "BASFI": basfi(v),
                "BASMI": {"score": v.basmi_total, "range": "0-10"},
            },
            "PROs": {
                "ASQoL": {"score": v.asqol, "range": "0-18 (0=best)"},
                "EQ-5D VAS": v.eq5d_vas,
            },
        })
    
    if len(visits) >= 2:
        asas = asas_response(visits[0], visits[-1])
        baseline_asdas = asdas_crp(visits[0])["score"]
        current_asdas = asdas_crp(visits[-1])["score"]
        delta = baseline_asdas - current_asdas
        results_t2t = {
            "ASDAS change": round(delta, 2),
            "Clinically important improvement (>=1.1)": delta >= 1.1,
            "Major improvement (>=2.0)": delta >= 2.0,
            "ASAS20": asas["ASAS20"],
            "ASAS40": asas["ASAS40"],
            "Target (inactive or low)": current_asdas < 2.1,
        }
    else:
        results_t2t = {"note": "Single visit"}
    
    return {"visits": results, "treat_to_target": results_t2t}


if __name__ == "__main__":
    print("=" * 70)
    print("AxSpA-MODEL: Axial Spondyloarthritis Disease Model")
    print("BASDAI + ASDAS + BASFI + BASMI + ASQoL + ASAS Response")
    print("=" * 70)
    
    visits = [
        AxSpAAssessment(visit="Baseline", basdai_q1_fatigue=7, basdai_q2_spinal_pain=8,
            basdai_q3_joint_pain=5, basdai_q4_enthesitis=6, basdai_q5_morning_stiffness_severity=8,
            basdai_q6_morning_stiffness_duration=7, back_pain=8, patient_global=7,
            peripheral_joint=5, morning_stiffness_duration=7, crp=28, esr=35,
            basfi_scores=[7,6,8,5,7,6,8,5,7,6], asqol=14, eq5d_vas=30, basmi_total=4.2),
        AxSpAAssessment(visit="Week 12", basdai_q1_fatigue=4, basdai_q2_spinal_pain=4,
            basdai_q3_joint_pain=3, basdai_q4_enthesitis=3, basdai_q5_morning_stiffness_severity=4,
            basdai_q6_morning_stiffness_duration=3, back_pain=4, patient_global=4,
            peripheral_joint=2, morning_stiffness_duration=3, crp=8, esr=15,
            basfi_scores=[4,3,5,3,4,3,5,3,4,3], asqol=8, eq5d_vas=60, basmi_total=3.5),
        AxSpAAssessment(visit="Week 52", basdai_q1_fatigue=2, basdai_q2_spinal_pain=2,
            basdai_q3_joint_pain=1, basdai_q4_enthesitis=1, basdai_q5_morning_stiffness_severity=2,
            basdai_q6_morning_stiffness_duration=1, back_pain=2, patient_global=2,
            peripheral_joint=1, morning_stiffness_duration=1, crp=3, esr=8,
            basfi_scores=[2,2,3,1,2,2,3,1,2,2], asqol=4, eq5d_vas=78, basmi_total=3.0),
    ]
    
    analysis = full_assessment(visits)
    
    for v in analysis["visits"]:
        print(f"\n{'─' * 50}")
        print(f"  {v['visit']}")
        a = v["activity"]
        print(f"  BASDAI: {a['BASDAI']['score']} ({a['BASDAI']['category']})")
        print(f"  ASDAS-CRP: {a['ASDAS-CRP']['score']} ({a['ASDAS-CRP']['category']})")
        f = v["function"]
        print(f"  BASFI: {f['BASFI']['score']} ({f['BASFI']['category']}) | BASMI: {f['BASMI']['score']}")
        p = v["PROs"]
        print(f"  ASQoL: {p['ASQoL']['score']}/18 | EQ-5D: {p['EQ-5D VAS']}")
    
    t = analysis["treat_to_target"]
    print(f"\n{'=' * 50}")
    print(f"  TREAT-TO-TARGET")
    for k, v in t.items():
        print(f"  {k}: {v}")
    
    print(f"\n{'=' * 70}")
    print("x402: Single <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mn>1.50</mn><mi mathvariant="normal">∣</mi><mi>L</mi><mi>o</mi><mi>n</mi><mi>g</mi><mi>i</mi><mi>t</mi><mi>u</mi><mi>d</mi><mi>i</mi><mi>n</mi><mi>a</mi><mi>l</mi></mrow><annotation encoding="application/x-tex">1.50 | Longitudinal</annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:1em;vertical-align:-0.25em;"></span><span class="mord">1.50∣</span><span class="mord mathnormal">L</span><span class="mord mathnormal">o</span><span class="mord mathnormal">n</span><span class="mord mathnormal" style="margin-right:0.0359em;">g</span><span class="mord mathnormal">i</span><span class="mord mathnormal">t</span><span class="mord mathnormal">u</span><span class="mord mathnormal">d</span><span class="mord mathnormal">ina</span><span class="mord mathnormal" style="margin-right:0.0197em;">l</span></span></span></span>5.00 | Study $12.00 USDC")
    print("\nRefs:")
    print("  [1] Garrett S et al. J Rheumatol 1994;21:2286-91 (BASDAI)")
    print("  [2] Lukas C et al. Ann Rheum Dis 2009;68:18-24 (ASDAS) DOI:10.1136/ard.2008.094870")
    print("  [3] Calin A et al. J Rheumatol 1994;21:2281-5 (BASFI)")
    print("  [4] Ramiro S et al. Ann Rheum Dis 2023;82:19-34 (ASAS-EULAR T2T) DOI:10.1136/ard-2022-223296")
    print("=" * 70)

Demo output

======================================================================
AxSpA-MODEL: Axial Spondyloarthritis Disease Model
BASDAI + ASDAS + BASFI + BASMI + ASQoL + ASAS Response
======================================================================

──────────────────────────────────────────────────
  Baseline
  BASDAI: 6.7 (High activity (>=4 = biologic eligible))
  ASDAS-CRP: 4.46 (Very high activity)
  BASFI: 6.5 (Moderate impairment) | BASMI: 4.2
  ASQoL: 14/18 | EQ-5D: 30

──────────────────────────────────────────────────
  Week 12
  BASDAI: 3.5 (Moderate activity)
  ASDAS-CRP: 2.52 (High activity)
  BASFI: 3.7 (Good function) | BASMI: 3.5
  ASQoL: 8/18 | EQ-5D: 60

──────────────────────────────────────────────────
  Week 52
  BASDAI: 1.5 (Low activity)
  ASDAS-CRP: 1.4 (Low activity)
  BASFI: 2.0 (Good function) | BASMI: 3.0
  ASQoL: 4/18 | EQ-5D: 78

==================================================
  TREAT-TO-TARGET
  ASDAS change: 3.06
  Clinically important improvement (>=1.1): True
  Major improvement (>=2.0): True
  ASAS20: True
  ASAS40: True
  Target (inactive or low): True

======================================================================
x402: Single <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mn>1.50</mn><mi mathvariant="normal">∣</mi><mi>L</mi><mi>o</mi><mi>n</mi><mi>g</mi><mi>i</mi><mi>t</mi><mi>u</mi><mi>d</mi><mi>i</mi><mi>n</mi><mi>a</mi><mi>l</mi></mrow><annotation encoding="application/x-tex">1.50 | Longitudinal</annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:1em;vertical-align:-0.25em;"></span><span class="mord">1.50∣</span><span class="mord mathnormal">L</span><span class="mord mathnormal">o</span><span class="mord mathnormal">n</span><span class="mord mathnormal" style="margin-right:0.0359em;">g</span><span class="mord mathnormal">i</span><span class="mord mathnormal">t</span><span class="mord mathnormal">u</span><span class="mord mathnormal">d</span><span class="mord mathnormal">ina</span><span class="mord mathnormal" style="margin-right:0.0197em;">l</span></span></span></span>5.00 | Study $12.00 USDC

Refs:
  [1] Garrett S et al. J Rheumatol 1994;21:2286-91 (BASDAI)
  [2] Lukas C et al. Ann Rheum Dis 2009;68:18-24 (ASDAS) DOI:10.1136/ard.2008.094870
  [3] Calin A et al. J Rheumatol 1994;21:2281-5 (BASFI)
  [4] Ramiro S et al. Ann Rheum Dis 2023;82:19-34 (ASAS-EULAR T2T) DOI:10.1136/ard-2022-223296
======================================================================

Clinical significance

Axial spondyloarthritis management is often fragmented across symptom scales and inflammation markers. AXSPA-MODEL makes the trajectory visible in one place and supports treat-to-target discussion.

Limitations

• No imaging layer (MRI/X-ray) is included.
• BASFI/BASMI remain user-entered approximations.
• This is not a prognostic calibration study.
• It should not override specialist assessment or local protocols.

References

1. Lukas C, et al. ASDAS development. Ann Rheum Dis. 2009. DOI: 10.1136/ard.2008.094870
2. Ramiro S, et al. ASAS-EULAR recommendations for management and treat-to-target in axial spondyloarthritis. Ann Rheum Dis. 2023. DOI: 10.1136/ard-2022-223296
3. Reveille JD, et al. Measures of symptoms and disease status in ankylosing spondylitis. Arthritis Rheum. 2005. DOI: 10.1002/art.20575
4. Braun J, et al. Ankylosing spondylitis measures: ASQOL, BASDAI, BASFI, BASMI. Arthritis Rheum. 2005. DOI: 10.1002/art.11412