Posttransplant tumors are one of the important long-term complications of renal transplant. However, aside from noninvasive Kaposi sarcomas, increased production of benign tumors has not been observed after renal transplantation, and to our knowledge, no cases of posttransplant osteoid osteoma have been reported so far. Osteoid osteoma is a common, benign, bone neoplasm that occurs typically in the long bones and presents with severe, intractable pain.

Here, we present a 49-year-old man, who presented with increasing bone pain in the right upper arm, 7 months after a renal transplant. Despite an initial normal right humerus radiograph, a raised subperiosteal tumor was diagnosed in the medial border of the right humerus a few months later. An excisional biopsy was performed, and the pathologic report was an osteoid osteoma. The patient’s pain, which had been resistant to most analgesics, completely disappeared after surgery, and he is currently devoid of any lesions, 9 months after excision of the tumor.

Key words : Posttransplant malignancy, Osteoid osteoma, Post trasnplant, Tumors

Instroduction

Posttransplant tumors are a significant long-term complication of renal transplantation. They may arise de novo, may be transmitted from the donor, or may be due to recurrence of a previous tumor (1). Long-term immunosuppressive therapy increases the risk of tumor 100 times and the risk is correlated with the level of immunosuppression (2). Aside from noninvasive Kaposi sarcomas, increased rate of production of benign tumors has not been observed after renal transplantation and to our knowledge, no cases of posttransplant osteoid osteoma have been reported to date. Here, we present a 49-year-old man, who presented with increasing bone pain in the right upper arm, 7 months after a renal transplantation.

Case Presentation
In June 2006, a 49-year-old man was referred to the nephrology clinic of Hasheminejad Kidney Center for a kidney transplant. He reported an increased serum creatinine level of 3 mg/dL from 3 years before referral, which had occurred after a severe electrical burn. He developed end-stage renal disease 4 months before the referral, and regular hemodialysis had been instituted since that time.

The patient received a renal allograft from a living-unrelated man in July 2006. The transplant procedure was uneventful, and the patient was discharged 2 weeks later with a serum creatinine level of 1.4 mg/dL. He was on prednisolone (30 mg/day, decreased to 10 mg/day in 6 months, and 5 mg/day at 1 year), mycophenolate mofetil (2 g/day), and cyclosporine (300 mg/day). His serum creatinine level decreased to 1.2 mg/dL in 3 months. Seven months after the transplant, he was hospitalized for 7 days for treatment of herpes zoster on the right buttock region with intravenous acyclovir. After discharge, he started to complain of right upper limb pain. No signs of phlebitis or other lesions were seen, and local therapy was not effective. The pain increased during the next month with maximal severity in the right upper humerus region. The results of a plain radiograph of the humerus were normal.

Two months after the previous admission (9 months posttransplant), his serum creatinine level increased to 1.4 mg/d, the patient had a severe pain in the right humerus and an ulcer in the anal region. A polymerase chain reaction for cytomegalovirus was positive, and the patient was admitted for treatment of cytomegalovirus infection with intravenous ganciclovir. The anal ulcer was diagnosed as a genital wart and local podophyllin and benzoin were started. Meanwhile, an isotope bone scan showed increased uptake in the upper humerus region. Prednisolone was decreased to 5 mg/day, cyclosporine to 250 mg/d (C0 level kept at about 200 ng/mL), and the patient was referred to the orthopedic ward. No specific diagnosis was made, and a local injection of steroid was administered with no clinical improvement. The patient refused another orthopedic consult and was discharged after 3 weeks of intravenous ganciclovir treatment.

In the subsequent 3 months, his serum creatinine gradually increased to 1.75 m/d, and the severity of his upper limb pain waxed and waned. A repeat plain radiograph showed a raised lesion at the medial border of the right humerus, which was confirmed by CT scan and shown to have a nidus (Figure 1). A renal biopsy was done, and mild, patchy, acute rejection (Banff 1) with negative C4d staining was reported. A 3-day course of intravenous methylprednisolone was administered, which decreased his serum creatinine level to 1.1 mg/day.

A repeat plain radiograph after 2 months showed a raised lesion in the medial border of the right humerus. He was referred for orthopedic consultation, a benign tumor was diagnosed, and surgical resection was performed. Surgery showed a sclerotic lesion of the antero-lateral border of the right humerus with a hypodense nidus. Pathology reported an irregular, tan-brown tissue with bony consistency measuring 1.5 x 1 x 0.5 centimeters, which microscopically revealed a nidus of osteoid osteoma consisting of an interlacing network of osteoid and bony trabeculae with a rim of single layer of osteoblasts without atypia, showing variable mineralization (Figure 2). The pathologic diagnosis was an osteoid osteoma. The patient’s pain, which was resistant to most analgesics, completely disappeared after surgery, and he is devoid of any lesions at present, 9 months after excision of the tumor.

Discussion

Osteoid osteoma is a benign bone neoplasm that typically occurs in the long bones, such as the tibia or the fibula. It is a common lesion, constituting one-eighth of the benign bone tumors (3). The tumor is extremely painful with the pain often worse at night and usually relieved by salicylates (4). Osteoid osteoma usually occurs in the second and third decades of life (5). Male patients are more often affected than female patients with a ratio of 2:1 (5). Radiologically, an osteoid osteoma has a typical appearance of cortical thickening and sclerosis. If the “nidus” is not apparent on the plain radiographs, it will be identified on a CT scan (6). Surgical treatment including excision of the nidus is usually curative and is the treatment of choice (5).

To our knowledge, despite the increase in the frequency of many tumors after organ transplantation, no cases of posttransplant osteoid osteoma have been reported so far. As osteoid osteoma is a common bone tumor, our case may have been a clinical coincidence; however, the occurrence of the lesion 7 months after transplant in addition to the relatively high age of the patient for osteoid osteoma—which typically occurs in the second and third decades of life and is extremely rare over age 30 (7)—makes us to consider a possible role for immunosuppressive drugs. As this benign tumor was totally removed surgically, and there are no symptoms or signs of recurrence 9 months postoperatively, we did not further decrease the dosage of immunosuppressive drugs and will continue the patients' follow-up.

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