A 28 years old woman having limited cutaneous scleroderma for the last 10 years complains of shoness of breath for last one month. Her pulmonary function tests (PFT) are a following: PFT Observed Predicted FVC 2.63 2.82 FEV1 88% 80% DLCO 5.26 16.3 Which of the following is the most probable diagnosis in this patient?