Although any of the collagen vascular diseases can cause periungual telangiectases (the plural of telangiectasia is telangiectases, not telangiectasias) the classic association is with dermatomyositis, since DM is almost universally associated with those findings, as opposed to scleroderma, SLE, and the other CVDs. I did, however, give credit for any of the CVDs.
The most common of the lab tests to be positive for DM is creatine phosphokinase (CPK) but aldolase, Jo-1, ANA or any one of a number of lab tests can be considered to be extremely common with DM. Name three autoantibodies associated with DM for three points. Also, abnormal EMGs would be considered an abnormal lab test, as would an abnormal muscle biopsy.
The classic skin findings for DM (other than periungual telaingiectases) are heliotrope rash (swelling and violaceous changes of the upper lids) and Gottron's papules. Also, photosensitivity, urticarial changes, alopecia, fingertip ulceration, Raynaud's Phenomenon, hyperpigmentation and calcification may occur.