Peripheral vascular diseases always or only sometimes predicts carotid disease?

Sometimes. Athersclerosis is a systemic disease. This means it can affect any and all arteries. Having evidence of atherosclerosis in any arterial bed increase the risk of having it in others. However, it is not uncommon to find atherosclerosis affecting only certain arteries (legs) and not others (carotids). Why this occurs is not fully understood. If you have pad, you have 2x the risk of stroke or mi.
Sometimes . We often look for carotid disease as if it is inevitable, but it is not. Having peripheral vascular disease(pvd) increases your risk of stroke by 2-3x based on a recent paper, so it is always worth getting an ultrasound of the carotid arteries if you have pvd.