An elderly female presents with rash, limb myasthenia for 1 month, dysphagia, and chest tightness for half a month. Physical examination reveals violaceous patches on the upper eyelids with periorbital edema, coarse breath sounds in both lungs, fine moist rales in the lower lungs, tenderness in the left hand's 2nd and 4th PIP joints, muscle strength grade 3 in upper limbs, and grade 2 in lower limbs. Investigations show weakly positive ANA (1:100), negative ENA profile, elevated CK (4487 U/L), and chest CT scan suggesting pulmonary inflammatory changes. Dermatomyositis (DM) with pulmonary inflammation is suspected. To improve prognosis, what must be excluded concurrently when diagnosing DM?