Periostitis is a condition that describes inflammation of the periosteum which is a layer of dense connective tissue enveloping the bones. Periostitis may appear in various conditions, but trauma and infections are the most common causes. The diagnosis can be made through patient history, radiography, and magnetic resonance imaging.
The clinical presentation of periostitis may depend on the underlying cause but in most cases, local pain and swelling of the adjacent tissue are present. Additional symptoms of fever, chills, and profound tenderness are suggestive of an infectious etiology, most notable being osteomyelitis, secondary syphilis, actinomycosis (when periostitis of the mandible is seen) or odontogenic infections . In the setting of medial tibial stress syndrome (MTSS) (known as "shin splints”), inflammation of the periosteum leads to the appearance of vague and diffuse pain in the lower extremity, usually in the middle or distal tibia, which is provoked by exertion . In the early stages, pain is worse when starting the exercise and then gradually decreases during training and within minutes of stopping the exercise. However, as the injury progresses, pain occurs with less activity and may even occur at rest. . A similar clinical course can be observed in malignant or autoimmune diseases involving the skeletal system (e.g. leukemia, reactive arthritis, lung cancer with metastatic dissemination in the bones)  . In rare cases, multifocal periostitis involving more than one extremity (or even the axial skeleton) and diffuse pain can be seen in patients who are receiving long-term prophylaxis of voriconazole, as this antifungal drug contains fluoride, which is known to induce a periosteal reaction  .
Patient history is quite important in evaluating the etiology and course of the disease-causing the symptoms reported by the patient, especially when information such as recent voriconazole use or presence of malignant diseases are obtained. The diagnosis of periostitis as an isolated finding, however, can only be made through imaging studies. Radiography is an easy, effective and quick method to detect some of the key features that support the diagnosis. Irregular nodular calcifications along the interosseous membrane, edema of the periosteum, the presence of exostoses (an exuberant growth of periosteal bone due to inflammation), gross thickening of the affected bones, and a periosteal reaction of various types (single layer, onion skin, sunburst type, etc) are the main findings   . In fact, the type of periosteal reaction can be helpful, as "onion skin" type is typical for periostitis ossificans, a type of non-suppurative osteomyelitis , and for malignant neoplasms (Ewing's sarcoma, for example), whereas "sunburst" reaction is primarily encountered in benign tumors, such as osteoblastoma  . More advanced imaging studies - magnetic resonance imaging (MRI) or computed tomography (CT), or nuclear bone scanning, can be useful for determination of the cause, and to assess the state of the surrounding soft tissue .