Peripheral Arterial Disease (PAD): The patient's symptoms of pain in the calf region and thighs on walking, known as intermittent claudication, are classic for PAD, a common macrovascular complication of diabetes mellitus (DM). The pain is relieved by rest and recurs with walking, which is a hallmark of this condition.

Diabetic Neuropathy: While typically presenting with numbness, tingling, or burning sensations, in some cases, diabetic neuropathy can cause pain in the legs. However, the pain pattern usually differs from that of PAD.
Musculoskeletal Conditions: Conditions like osteoarthritis or muscle strain could cause leg pain but typically do not present with the specific pattern of pain on walking and relief with rest seen in PAD.

Aortic Dissection: Although rare, aortic dissection can present with acute onset of severe pain and should be considered, especially if the pain is severe and not typical for PAD.
Deep Vein Thrombosis (DVT): DVT can cause leg pain and swelling, and while it doesn't typically cause claudication, it's a critical diagnosis to consider due to the risk of pulmonary embolism.
Acute Limb Ischemia: This is a medical emergency that can present with severe limb pain, pallor, pulselessness, poikilothermia, paresthesias, and paralysis. It requires immediate intervention.

Chronic Compartment Syndrome: This condition can cause leg pain with activity but is less common and typically presents in younger individuals.
Popliteal Artery Entrapment Syndrome: A rare condition where the popliteal artery is compressed, leading to claudication, but it is more common in younger athletes.
Buerger's Disease (Thromboangiitis Obliterans): A rare disease of the arteries and veins in the arms and legs, which can cause claudication, but it is strongly associated with smoking and typically affects younger individuals.