Tuberculosis is caused by the myobacteria. TB can affect lungs, skin, liver, CNS, joints, GI tract, lymphatic system and bones etc. Rash on the legs is not symptom of any form of TB. Even skin TB does not cause rash. Skin TB causes lesions, papules, nodules, etc. Symptoms of lung TB are cough which last for more than 3 weeks, night sweats, fever especially at night, chills, weight loss and coughing up blood. Rashes on legs can be due to allergy, insect bite, side effects of medicines etc. You should visit a doctor for proper diagnosis and treatment of your problem.