**3. Laboratory findings**

#### **3.1 Pulmonary function tests**

Pulmonary function tests (PFT) provide objective evaluation of respiratory symptoms and are important in determining the disease activity and therapeutic effects. However, in patients with severe respiratory failure such as that in RPIP, the tests cannot be performed or the results are not determined. Typically, a restrictive ventilatory impairment is present, and total lung capacity (TLC), vital capacity (VC), forced vital capacity (FVC), and the diffusing capacity for carbon monoxide (DLco) are decreased (Fathi, 2008). A decrease in DLco is one of the most sensitive indices showing a decrease in gas exchange. These abnormalities are improved by treatment. In cases without IP but with decreased FVC, it is necessary to also consider a decrease in ventilatory muscle strength.

#### **3.2 Diagnostic Imaging**

For imaging assessment of IP, the sensitivity of the chest X-ray is lower than that of highresolution CT (HRCT) using less than 3-mm slices (Figure 1). When PM/DM or IP associated with PM/DM is suspected, the lung should be assessed by HRCT. However, because the chest X-ray is easy to use and radiation exposure is low, it is useful for following the course of the disease and for diagnosing complications such as infection.

HRCT findings observed in PM/DM are diverse. The most frequently observed findings are reticular opacity or ground-glass opacity with subpleural curvilinear shadow that is predominantly distributed just below the bilateral dorsal regions of the lungs, and the findings sometimes accompany consolidation (Mino, 1997, Douglas, 2001, Arakawa, 2003, Bonnefoy, 2004, Hayashi, 2008). Ground-glass opacity and consolidation are improved by treatment. The decreased lung volume and traction bronchiectasis (TBE) are sometimes observed, but patients with honeycomb lung are rare. It is difficult to predict the prognosis of IP associated with DM/PM and to select treatment based only on HRCT findings. However, HRCT are useful for the assessment of disease activity and therapeutic effect. IP that is distributed through a wide area of the lungs and accompanies TBE at the early onset or exacerbation has a poor prognosis.
