Varicose Vein Thrombophlebitis: This condition is characterized by inflammation of the vein wall and clot formation within a varicose vein, leading to tenderness, warmth, and swelling. It's a common complication of varicose veins and fits the symptoms described.

Superficial Thrombophlebitis: Inflammation of a superficial vein, which can be tender and may occur in the context of varicose veins, especially if there's an underlying condition like a blood clot.
Varicose Eczema (Stasis Dermatitis): While not directly causing tender varicose veins, the inflammation and skin changes associated with varicose eczema can lead to discomfort and tenderness in the affected area.
Lipodermatosclerosis: A condition characterized by inflammation and scarring of the subcutaneous fat, often associated with chronic venous insufficiency and varicose veins, leading to pain and tenderness.

Deep Vein Thrombosis (DVT): Although DVT typically presents with swelling, warmth, and pain in the affected limb without necessarily being confined to the area of a varicose vein, it's crucial to consider due to its potential for severe complications like pulmonary embolism.
Cellulitis: A bacterial infection of the skin and subcutaneous tissues that can present with redness, warmth, swelling, and tenderness, which might be mistaken for a complication of varicose veins.

Klippel-Trenaunay Syndrome: A rare congenital condition characterized by varicose veins, port-wine stains, and soft tissue or bony hypertrophy, which could potentially cause tender varicose veins among other symptoms.
Malignant Transformation of Varicose Veins: Extremely rare, but varicose veins can very occasionally be associated with malignant changes, such as angiosarcoma, which would present with unusual or unexplained pain and tenderness.