Epidemiology of interstitial lung disease associated with connective tissue disease in Canterbury

Project brief

Introduction

The prevalence of interstitial lung disease (ILD) associated with connective tissue disease (CTD) including rheumatoid arthritis (RA) is unknown in Canterbury and New Zealand. Outpatient ILD diagnoses are not coded making us reliant on inpatient coding which underestimates the true impact of disease. In addition, many CTD patients have sub-clinical ILD and the forme fruste presentation of a CTD-ILD evades diagnosis unless the respiratory physician has a high index of suspicion. Prevalence estimates from around the world range between 2.39 to 12 cases per 100,000 population (1,2). No epidemiological data exists in New Zealand regarding the prevalence of CTD-ILD in Māori or Pacific Islanders. Wilsher et al observed that in an Auckland ILD cohort there were very few Māori Patients with idiopathic pulmonary fibrosis (3) and that Māori and Pacific Island patients were less likely to develop ILD when diagnosed with sarcoidosis (4). It is uncertain whether this is related to a protective phenomenon or reflects differences in access to care.

In patients presenting with respiratory symptoms and CT evidence of ILD early studies have found that CTD-ILD was the cause in 8.9%-14.8% of cases (1,2). More recently 30% of ILD cases were found to have an underlying connective tissue disease (5). The early identification of an underlying CTD is important in therapeutic decision making and usually has an impact on prognostication.

However, the optimum management of CTD-ILD patients with progressive fibrotic lung disease is uncertain. In rheumatoid arthritis in particular when there is evidence of progressive fibrotic lung disease patients have a mortality very similar to that of idiopathic pulmonary fibrosis (IPF) (6). The results from trials using anti-fibrotic medication alone or in combination with immunomodulatory therapy are urgently awaited.

This summer studentship will form the basis of a long-term project on ILD in Canterbury. The student will be responsible for identifying all patients in Canterbury with a radiological diagnosis of interstitial lung disease over the last 10 years. This will allow them to determine the prevalence of CTD-ILD and elucidate whether ethnicity and in particular Maori descent offers protection against development of ILD.

Aim

1. To identify all patients with radiological evidence of interstitial lung disease in Canterbury according to ethnicity.
2. To identify the proportion of patients with radiological evidence of ILD and a diagnosis of connective tissue disease.
3. To identify the proportion of patients with radiological evidence of ILD with auto-immune features (clinical, serological, radiology or pathology) who do not meet criteria of a defined connective tissue disease.

Method

This is a retrospective observational study of all patients living in Canterbury with a radiological diagnosis of ILD between July 1st 2008 and July 1st 2018. The radiology database will be interrogated for patients with a radiological report stating interstitial lung disease (on chest X-ray, CT chest or CT abdomen capturing the lung bases). The clinical information entered at the time of radiology request will define whether patients had respiratory symptoms at the time of the investigation or whether the ILD was an incidental finding. The proportion of patients with this radiological diagnosis that were subsequently reviewed by a respiratory physician, general physician, rheumatologist and the number that had no subsequent follow up (sub-clinical disease).

1. Demographic details: age, ethnicity, sex, occupation exposure, smoking history, pets / bird exposure.
2. Rheumatologic symptoms / examination
3. Respiratory investigations: spirometry, lung volumes, dlco, kco, pulse oximetry, ABG, 6 minute walk test
4. Echocardiogram
5. Blood tests: FBC, Renal function,CK, urine biochemistry / microscopy (red cells casts) and Autoimmune serology including ANA, anti CCP, RhF, ANCA, dsDNA, ENA, myositis screen, serum ace, immunoglobulins

Outcome measures

Was there a confirmed diagnosis of CTD-ILD 6/12 post radiology report.

The population in Canterbury will be taken from the most recently available census and the prevalence will be calculated. The prevalence by ethnicity will also be determined.

Student researcher’s component of the study

The student will be required to review the medical records of all those identified in the radiology database. They will collect and record the following information in an electronic data base. They will calculate the prevalence of ILD. And describe the basic demographic and clinical characteristics of the population in Canterbury.

References

1. Coultas et al. American journal of respiratory and critical care medicine 150 (4), 967-972,1994.
2. Denedts et al. European Respiratory Journal 18 (32 suppl),2s-16s,2001.
3. Wilsher et al. Respirology 22 (2), 360-363,2017.
4. Young et al. Respirology 11 (4), 467-470,2006.
5. Mittoo et al. Respiratory Medicine 103 (8),1152-1158,2009.
6. 6Solomon et al. European Respiratory Journal 47 (2), 588-596.