[RARE LOCALIZATION OF OSTEOID OSTEOMA--DISTAL PHALANX OF THE RING FINGER].

: With this clinical observation we would like to bring to mind osteoid osteoma as a possible cause of problems of distal phalanx of the fingers. Osteoid osteoma occurs rarely at this location and has atypical presentation. The main symptoms are swelling and redness of the fingertip with nail deformity, while typical night pain may not be present. Unusual clinical and x-ray presentation of tumor in this localization can make diagnosis of osteoid osteoma very difficult. A 20-year-old patient reported pain in the fingertip of his right ring finger persisting for five years. Swelling and redness of the fingertip combined with nail deformity was also present. X-rays showed osteolysis in the base of distal phalanx. Magnetic resonance imaging showed suspicion of osteoid osteoma, which was confirmed by computed tomography (CT). We performed surgical removal of osteoid osteoma in February 2014. The tumor was approached by longitudinal incision on the lateral side of the distal phalanx of the ring finger and the basal part of distal phalanx was cut with a small chisel to enable access to cystic change of the bone. Tumor removal with excochleation was performed and the material thus obtained was sent for histopathologic analysis. After surgery, the ring finger was immobilized in a plaster splint for a three-week period. After removal of immobilization, the patient was referred to physical therapy consisting of individual exercises in order to obtain the full range of motion in all joints of the hands and strengthen hand and forearm muscles. After surgical removal of osteoid osteoma, all symptoms disappeared completely. Histopathologic findings confirmed the diagnosis of osteoid osteoma. After physical therapy, he returned to daily activities without any problems. On regular follow ups at 3, 6 and 12 months after surgery, clinical findings were normal and the patient had no pain or discomforts. Full recovery was shown by the result of the DASH questionnaire three months after the procedure. Preoperative DASH score 54.4 decreased to 0. Distal phalanx of the finger is a very rare localization of osteoid osteoma, and typical night pain may not be present. In addition, appearance on x-rays is not typical. Instead of central enlightenment surrounded with sclerosis, x-rays usually show a lytic lesion. For this reason, it may be difficult to make the diagnosis of osteoid osteoma. The main symptom is permanent pain, swelling and redness of the finger, with nail deformity. The imaging method of choice is CT, which must be performed with thin layers of 1 to 2 mm. Furthermore, cooperation of surgeon and radiologist is extremely important to reach the accurate diagnosis. Many treatment options are described in the literature, such as CT-guided percutaneous thermocoagulation, destruction of lesions with alcohol, or CT-guided radiofrequency ablation. However, due to the proximity of neurovascular structures, tendons and joints, the best method for treatment osteoid osteoma in distal phalanx of the fingers is surgical excision or excochleation. Our conclusion is that one should always bear in mind that osteoid osteoma can be the cause of swelling of distal phalanx of the finger with nail deformity, and pain that alleviated with the use of non-steroidal anti-infl ammatory drugs. Surgical excision or excochleation is the best method for the treatment osteoid osteoma of distal phalanx of the finger.