Warning signs of interstitial lung disease appear in primary care records as early as 10 years before a diagnosis, yet almost all patients who end up having the condition receive an alternative diagnosis first, Australian-led research has found.

Writing in the journal Respirology [link here], the research team, led by respiratory physicians at the Royal Prince Alfred Hospital, Sydney, alongside UK colleagues, said improving awareness of ILD among GPs could be key to avoiding misdiagnosis, shortening diagnosis delays and expediting access to treatments.

Using a UK health record database, they followed 18,914 patients with ILD from January 2010 to December 2019, comparing the presentations of these patients to those of 60,156 matched controls. The dates were selected to avoid the impact of COVID-19.

The ILD cohort was made up of hypersensitivity pneumonitis (HP) cases (9%), connective tissue disease-­related ILD (CTD-ILD) cases (28%) and idiopathic pulmonary fibrosis (IPF) cases (63%).

Findings showed dyspnoea, cough, fatigue, weight loss and loss of appetite were all recorded more frequently among ILD patients versus controls in the year preceding diagnosis. Patients with ILD were also more likely to have crackles on lung auscultation, have a heart failure diagnosis or a chest x-­ ray performed.

Cough was the most common symptom coded in HP and CTD-­ ILD cases, whereas dyspnoea was most often recorded in IPF cases, the researchers said.

Overall, most patients (73%) reported cough or dyspnoea in at least one GP visit, with 13%-17% recording symptoms on at least five separate occasions (dyspnoea: 13% cases vs 5% controls; cough: 17% cases vs 7% controls).

Patients with ILD had a greater cumulative incidence of cough and dyspnoea even 10 years before diagnosis (OR: 1.73 [1.58, 1.89], p < 0.001), with the odds ratio increasing to 2.38 at one year before diagnosis (CI: 2.27–2.49, p < 0.001).

When it came to diagnosis, 97% of ILD cases had been previously diagnosed with another respiratory disease a median of 3.8 years before their ILD diagnosis, while 4% of patients had received a heart failure diagnosis.

The researchers pointed out that cough and breathlessness were non-­specific symptoms and it was understandable that GPs would first consider more prevalent conditions, such as asthma, COPD or heart failure over a rare condition like ILD.

However, in doing so, unnecessary investigations or treatment could delay ILD diagnosis and treatment, missing the opportunity to prevent further fibrosis, they said.

They suggested an automatic warning flag embedded into GP software might be useful for prompting GPs to consider ILD when specific signs and symptoms were repeatedly present, or to pursue additional investigations such as spirometry.

“A more detailed assessment of symptoms, such as chronological patterns of cough, may be useful for differentiating conditions such as asthma and ILD, as nocturnal cough is more prevalent in asthma,” the researchers also noted.

“Similarly, lung auscultation for the detection of fine crackles is a simple technique enabling early ILD diagnosis and differentiation between some cardiorespiratory conditions with overlapping symptoms. However, expanding awareness of their diagnostic relevance in primary care may be needed.”