I Musculoskeletal/neural A Muscle Trauma—contusions, lacerations, strain Infection—myositis B Breast Physiologic (fullness during menses or pregnancy) Mastitis Fibrocystic disease Tumor (adenoma, other) Gynecomastia C Bone Trauma—contusions, rib fractures Osteitis, osteomyelitis Costochondritis, Tietze syndrome Tumor Slipping rib syndrome D Intercostal nerve Neuritis—zoster, trauma Toxin E Dorsal root Trauma Radiculitis—viral, postviral Spinal disease—scoliosis II Tracheobronchial (proximal bronchi) A Foreign body B Infection Tracheitis Bronchitis Cystic fibrosis C Asthma III Pulmonary/pleural/diaphragm A Trauma—penetrating and blunt B Pleurisy/pleurodynia—viral, mycobacterial C Pneumonia D Cystic fibrosis E Pneumothorax, hemothorax, chylothorax