Are telangiectasias pathognomonic for a certain disease?

No. Telangiectasias may occur in many cutaneous disorders, including collagen vascular diseases such as dermatomyositis, systemic lupus erythematosus, and progressive systemic sclerosis. They are also commonly seen as a consequence of chronic ultraviolet radiation and topical steroid usage. Telangiectasias may also be seen in tumors such as a noduloulcerative basal cell carcinoma, which is classically described as a pearly colored papule with telangiectasias and central ulceration.