Erythema nodosum: This is a common condition characterized by the sudden onset of tender, erythematous nodules on the lower extremities, often associated with an underlying infection, inflammatory disease, or drug reaction.

Cellulitis: An infection of the skin and subcutaneous tissue, which can present with nodular lesions, especially if there is an abscess formation.
Folliculitis: Inflammation of the hair follicles, which can cause nodular lesions on the legs, particularly in areas prone to shaving or friction.
Keratosis pilaris: A benign condition characterized by small, rough, sandpaper-like nodules on the skin, often on the legs, due to excess keratin.

Deep Vein Thrombosis (DVT): Although DVT typically presents with swelling, warmth, and discoloration of the leg, it can occasionally cause nodular lesions if there is associated thrombophlebitis or venous ulceration.
Malignancy (e.g., lymphoma, metastatic disease): Rarely, nodules on the legs can be a manifestation of an underlying malignancy, making it crucial to investigate further if other symptoms or risk factors are present.
Infectious diseases (e.g., tuberculosis, leprosy): Certain infectious diseases can cause nodular skin lesions on the legs, and missing these diagnoses could have significant consequences.

Panniculitis: Inflammation of the subcutaneous fat, which can cause nodular lesions on the legs, often associated with systemic diseases or drug reactions.
Necrobiosis lipoidica: A rare condition characterized by necrotic, granulomatous lesions in the skin, often on the lower legs, associated with diabetes mellitus.
Sarcoidosis: A systemic granulomatous disease that can cause skin nodules, including on the legs, although this is less common.