1. Case presentation By Bassma Elnaggar MD Rheumatology & rehabilitation Al-Azhar univerisity

2. History Female patient, 25 years old, student, lives at Helwan, single, with no special habits of medical importance. The patient presented to outpatient clinic by pain of right shoulder of gradual onset and progressive course for 5 months for duration.

3. History The pain is dull aching in character more at night, not related to physical activity and partially respond to analgesics. No, history of direct or indirect trauma, and no constitutional manifestations or weight loss. The patient is known to be RA for 9 years duration and her arthritis distribution is oligoarticular affecting mainly Rt shoulder, Lt Knee, and Lt elbow.

4. History The patient asked medical advice for the RT shoulder pain before 2 months and received intra- articular injection of steroid with no improvement. The patient is on medical treatment leflunamide 20 mg\day, hydroxychloroquine 200mg\day and prednisone 5mg\day. The patient has family history of osteosarcoma in second degree relative.

5. Examination On examination the patient was systemically well, but local examination of Rt shoulder revealed wasting of muscles around the RT shoulder (supraspinatus, infraspinatus and deltoid), sever tenderness along joint line, and over deltoid muscle, painful limited active and passive range of motion in all directions, but no signs of inflammation.

6. Examination Lt elbow examination revealed mild tenderness along the joint line, chronic synovitis, and extension lag 10 degrees. RT knee examination : supra patellar swelling, mild tenderness along joint line, chronic synovitis, FROM, mild effusion. Other joint examination was normal. DAS28 score was 3.7 with moderate disease activity..

7. Examination Back examination revealed mild paraspinal muscle spasm and FROM of cervical and lumber spine. Neurological examination revealed muscle power grade 4 of mucles of RT upper limb.

8. Lab. Investigations Normal CBC with normal differential count Normal liver and kidney function tests Normal ESR 25 mm\hr Normal serum calcium and phosphrus levels Normal alkaline phosphatase level ml.\RF low titer 12 IU Anti CCP low titer (25 U\dl)

9. Radiological assessment Plain X ray was done for RT shoulder revealed osteolytic lesion of metaphysis and epiphysis of Rt humerus. The lesion was well demarcated with sclerotic margin.

11. We thought about potentional causes of osteolytic lesion in RA patients such as osteomyelitis, osteonecrosis, osteoid osteoma, osteoblastoma, pigmented villonodular synovitis and osteosarcoma or metastasis.

12. However, the absence of systemic manifestations of fever and weight loss in addition to normal laboratory findings exclude diagnosis of osteomyelitis, and osteosarcoma.

13. CT scan was done for the patient revealed well defined osteolytic lesion of humeral metapysis and subchondral bine cyst for clinical correlation and CT guided biopsy is recommended

15. CT guided true cut needle biopsy was done and sections revealed lamellar bone trabeculae rimmed with osteoblasts and woven bone with cystic changes.

16. Based on clinical, radiological and histopathological findings, benign bone lesions like osteoblastoma or osteoid osteoma is a probable diagnosis.

17.  Osteoblastoma is an osteoid tissue forming primary neoplasm of the bone, accounting for 0.5-2% of all primary bone tumors and 14% of benign bone tumors  Osteoblastoma can occur at any age, with more affection of younger population (around 80% of these tumors occurs in persons under the age of 30.

18.  Usual sites of osteoblastoma are in long bones or vertebral column.  The long bone affection is often diaphyseal, and fewer lesions are located in the metaphysis and epiphysis.  Spinal osteoblastoma usually involve posterior elements. causing painful scoliosis, and may mechanically interfere with the spinal cord or nerve root, producing neurologic deficits.

19. osteoblastoma patients usually present with pain for several months duration. The prostaglandins produced by the tumour directly stimulate the nerve endings by lowering the threshold of pain receptors. The pain is less intense than osteoid osteoma, does not increase at night initially and not relieved readily with salicylates.

20. Osteoblastoma has a greater potential for growth, with destruction of bone tissue or even malignant transformation. The sclerotic reaction is often milder in osteoblastoma than in osteoid osteoma.

21. Histologically, osteoblastomas are similar to osteoid osteomas, producing osteoid and woven bone within fibrovascular connective. The difference being that osteoblastoma can grow larger than 2.0 cm in diameter while osteoid osteomas cannot.

22. Mangment  Most authoritis believe that chemo and radiotherapy of osteoblastoma is controversial and has more risk than benefit.  Post irradiation osteosarcoma is a well documented outcome in mangment of benign tumour.

23. Mangment ○ Surgical excision is the treatment of choice of osteoblastomas and must be carefully planned for repairing the structural bony defect. ○ Pre and post operative rehabilitation is imporyant to maintain functional performance of upper limb.