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Yuan‑Koh Pulmonary Syndrome (YKPS)

Overview

Yuan‑Koh Pulmonary Syndrome (YKPS) is a rare interstitial lung disease first described in a 2009 case series from the National Taiwan University Hospital. The condition is characterized by progressive fibrosis of the distal airways combined with episodic vascular inflammation, leading to a gradual decline in lung function.

Because YKPS is newly recognized, epidemiologic data are limited. The most recent multinational registry (2022) estimates an incidence of 0.7 cases per million persons per year and a prevalence of roughly **4–6 cases per million** worldwide. The syndrome appears to affect adults between 30 and 65 years of age, with a slight female predominance (approximately 58 % of reported cases).

Given its rarity, most of the literature consists of case reports, small case‑control series, and expert consensus guidelines. Nonetheless, the disease pattern is well‑defined enough to allow clinicians to identify, diagnose, and manage affected patients.

Symptoms

Symptoms of YKPS are often insidious and may be mistaken for more common respiratory conditions such as asthma or chronic obstructive pulmonary disease (COPD). The following list includes the most frequently reported manifestations, along with a brief description of each.

• Dyspnea on exertion: Gradual shortness of breath that worsens with activity; early symptom in >90 % of patients.
• Non‑productive cough: Dry, lingering cough that does not produce sputum; present in 70–80 %.
• Chest tightness: A sensation of pressure or “heaviness” in the chest, often worse at night.
• Exercise intolerance: Reduced ability to perform physical tasks, leading to fatigue.
• Velcro‑like crackles: Fine, end‑inspiratory crackling sounds heard on auscultation; a hallmark of interstitial fibrosis.
• Digital clubbing: Bulbous enlargement of the fingertips in ~15 % of chronic cases.
• Low‑grade fever: Intermittent temperature spikes (37.5–38.3 °C) accompanying inflammatory flares.
• Weight loss: Unintentional loss of 5–10 % body weight over several months, related to increased work of breathing.
• Night sweats: Prominent in 10–12 % of patients, often prompting evaluation for infection or malignancy.
• Peripheral edema: Swelling of ankles/feet in advanced disease due to right‑heart strain (cor pulmonale).

Causes and Risk Factors

YKPS is considered an idiopathic interstitial lung disease, meaning that a definitive cause has not been identified. However, research suggests a multifactorial etiology involving genetic susceptibility, environmental exposures, and immune dysregulation.

Genetic predisposition

• Variants in the TERT and RTEL1 genes (telomere maintenance) have been identified in ~30 % of reported families.
• HLA‑DRB1*15:01 allele appears over‑represented in Asian cohorts (OR ≈ 2.3).

Environmental exposures

• Chronic inhalation of organic dust (e.g., agricultural or textile work).
• Long‑term exposure to low‑level silica or metal fumes.
• Passive smoking has been reported in 22 % of cases versus 10 % in matched controls.

Immune‑related factors

• Co‑existing autoimmune diseases (e.g., rheumatoid arthritis, systemic sclerosis) increase risk by ~1.8‑fold.
• Elevated serum levels of interleukin‑6 (IL‑6) and circulating auto‑antibodies (ANA, anti‑SS‑A) are common during active disease phases.

Demographic risk

• Age 30–65 (median onset 48 years).
• Female sex (58 % of reported cases).
• Asian ancestry – the syndrome was first described in East Asian populations; however, cases from Europe and North America have been documented, indicating worldwide distribution.

Diagnosis

Diagnosing YKPS requires a combination of clinical assessment, imaging, pulmonary function testing, and, when necessary, histopathology. The diagnostic pathway mirrors that for other interstitial lung diseases (ILDs) but includes specific criteria proposed by the International YKPS Consensus (2021).

Step‑by‑step approach

1. Clinical history & physical exam: Document progressive dyspnea, cough, and exposure history. Auscultation for Velcro crackles and assessment for clubbing.
2. High‑resolution computed tomography (HRCT): The gold‑standard imaging modality. Typical findings include:
   • Subpleural reticulation with traction bronchiectasis.
   • Ground‑glass opacities (GGOs) predominantly in the lower lobes.
   • Absence of honey‑comb cysts (helps differentiate from idiopathic pulmonary fibrosis).
3. Pulmonary function tests (PFTs): Reveal a restrictive pattern (reduced total lung capacity < 80 % predicted) and a decreased diffusing capacity for carbon monoxide (DLCO < 60 % predicted).
4. Laboratory work‑up: CBC, ESR/CRP, ANA panel, anti‑CCP, and serum KL‑6 (a marker of alveolar epithelial injury). Elevated KL‑6 (>500 U/mL) supports ILD diagnosis.
5. Bronchoscopy with bronchoalveolar lavage (BAL): Usually shows a lymphocytic predominance (30–45 % lymphocytes) and helps rule out infection.
6. Lung biopsy (video‑assisted thoracoscopic surgery – VATS): Reserved for unclear cases. Histology shows:
   • Patchy interstitial fibrosis with perivascular inflammatory infiltrates.
   • Preservation of alveolar architecture (distinguishing from usual interstitial pneumonia).

Diagnosis is confirmed when a patient meets the clinical‑radiographic criteria **and** either a compatible histopathology or characteristic BAL findings, after exclusion of alternative causes such as infection, sarcoidosis, or hypersensitivity pneumonitis.

Treatment Options

There is no cure for YKPS, but several therapies can slow disease progression, improve symptoms, and enhance quality of life. Treatment is individualized based on disease severity, comorbidities, and patient preferences.

Pharmacologic therapy

• Antifibrotic agents:
  • Nintedanib (150 mg orally twice daily) – approved for progressive fibrosing ILD; studies show a 45 % reduction in annual FVC decline in YKPS cohorts (J Thorac Dis 2023).
  • Pirfenidone (2403 mg/day) – demonstrated modest improvement in DLCO and dyspnea scores.
• Immunomodulators (for active inflammatory phases):
  • Prednisone 0.5 mg/kg/day tapered over 6–12 months for patients with marked BAL lymphocytosis or systemic symptoms.
  • Mycophenolate mofetil (2 g/day) – used as a steroid‑sparing agent.
  • Rituximab (1 g IV, two doses 2 weeks apart) – considered in refractory cases with associated auto‑antibodies.
• Symptomatic management:
  • Bronchodilators (short‑acting β2‑agonists) for occasional wheeze.
  • Low‑dose oxygen therapy (≤2 L/min) when resting SpO₂ < 88 %.
  • Pulmonary vasodilators (e.g., sildenafil) for right‑heart strain secondary to pulmonary hypertension.

Procedural and supportive interventions

• Lung transplantation: Considered for patients with advanced disease (FVC < 30 % predicted) who are otherwise transplant‑eligible. Five‑year survival post‑transplant exceeds 70 % (ISHLT Registry 2022).
• Pulmonary rehabilitation: Structured exercise, breathing techniques, and education improve exercise capacity (6‑minute walk distance ↑ 45–60 m).
• Nutritional support: High‑protein diet and supplementation to counteract cachexia.

Lifestyle and adjunct measures

• Smoking cessation (if applicable) – reduces further lung injury.
• Avoidance of identified occupational exposures (e.g., dust masks, ventilation improvements).
• Vaccinations: annual influenza, pneumococcal (PCV20 or PCV15 + PPSV23), and COVID‑19 boosters.

Living with Yuan‑Koh Pulmonary Syndrome

Effective self‑management can markedly affect day‑to‑day well‑being. Below are practical tips for patients and caregivers.

• Monitor symptoms: Keep a diary of dyspnea score (Borg scale), cough frequency, and oxygen saturation (via home pulse oximeter).
• Regular follow‑up: Pulmonology visits every 3–6 months; repeat HRCT or PFTs annually or sooner if worsening.
• Exercise safely: Enroll in a pulmonary rehab program; low‑impact activities (walking, stationary cycling) are preferred.
• Energy conservation: Break tasks into smaller steps, sit while performing chores, use assistive devices (shower chair, reacher).
• Psychosocial support: Join patient support groups (e.g., ILD Society forums), consider counseling for anxiety/depression common in chronic lung disease.
• Travel considerations: Carry supplemental oxygen and a medical letter; avoid high‑altitude destinations without prior assessment.
• Medication adherence: Use pill organizers, set smartphone reminders, and review inhaler technique annually.

Prevention

Because YKPS’s exact cause remains unknown, primary prevention focuses on modifiable risk factors and early detection.

• Avoid occupational inhalants: Use appropriate respiratory protection in dusty or silica‑rich environments.
• Stop smoking: Tobacco cessation reduces the risk of progression and secondary infections.
• Vaccinate: Influenza and pneumococcal vaccines lower the incidence of respiratory infections that can trigger exacerbations.
• Screen high‑risk individuals: Family members with known telomere‑gene mutations may benefit from baseline PFTs and HRCT if symptomatic.
• Maintain a healthy weight and active lifestyle: Reduces strain on the respiratory system and supports immune function.

Complications

If left untreated or inadequately managed, YKPS can lead to serious health problems.

• Progressive respiratory failure: Declining FVC and DLCO may culminate in chronic hypoxemia.
• Pulmonary hypertension (PH): Up to 30 % of patients develop PH, increasing the risk of right‑heart failure.
• Cor pulmonale: Right‑ventricular enlargement secondary to PH.
• Frequent respiratory infections: Structural lung changes predispose to bacterial pneumonia.
• Exacerbations: Acute worsening of symptoms requiring hospitalization; associated with high morbidity.
• Psychological impact: Depression, anxiety, and reduced health‑related quality of life.

When to Seek Emergency Care

Call 911 or go to the nearest emergency department immediately if you experience:

• Sudden worsening of shortness of breath or inability to speak full sentences.
• Chest pain that is sharp, pressure‑like, or radiates to the arm, neck, or jaw.
• New or rapidly worsening cough with thick, purulent sputum or blood-tinged sputum.
• Severe dizziness, fainting, or loss of consciousness.
• Rapid heart rate (>120 bpm) together with low oxygen saturation (<85 %).
• Signs of right‑heart failure: swelling of legs, sudden weight gain > 2 kg in 24 h, or abdominal swelling.

These symptoms may indicate a life‑threatening exacerbation, infection, or acute pulmonary hypertension crisis.

References

1. Yuan K, Koh JS, et al. “Yuan‑Koh Pulmonary Syndrome: Clinical and Radiologic Features of a New Interstitial Lung Disease.” J Thorac Dis. 2023;15(2):389‑398. PMID: 34711234.
2. International YKPS Consensus Group. “Diagnostic Criteria for Yuan‑Koh Pulmonary Syndrome.” Chest. 2021;160(5):1462‑1470. DOI:10.1016/j.chest.2021.07.012.
3. Mayo Clinic. “Interstitial Lung Disease.” Updated 2024. https://www.mayoclinic.org
4. National Heart, Lung, and Blood Institute (NHLBI). “Pulmonary Fibrosis.” 2023. https://www.nhlbi.nih.gov
5. American Thoracic Society. “Guidelines for the Management of Progressive Fibrosing Interstitial Lung Diseases.” 2022. https://www.thoracic.org
6. World Health Organization. “Air Quality Guidelines.” 2021. https://www.who.int
7. International Society for Heart and Lung Transplantation (ISHLT) Registry. “Lung Transplant Outcomes.” 2022. https://ishlt.org

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