Benign incidental findings of osteopoikilosis on Tc-99m MDP bone SPECT/CT

Abstract

Osteopoikilosis is a benign but rare condition characterized by bone islands throughout the osseous tissue, which could be easily confused with bone metastasis. We present a case of a 37-year-old man presented to orthopedic outpatient clinic with right hip pain for 2 weeks. There were multiple, small punctate lesions scattered throughout the skeleton on radiograph. Subsequent Tc-99m methylene diphosphonate (MDP) bone scan with pelvic single-photon emission computed tomography (SPECT)/computed tomography (CT) showed multiple enostoses without abnormal focal MDP uptake. Therefore, clinical diagnosis was compatible with osteopoikilosis while bone metastasis was unlikely. The symptoms then improved by conservative treatments. Osteopoikilosis is usually an incidental finding on radiograph or CT, and a normal MDP confirmed the diagnosis by excluding bone metastasis. It is important for clinicians to recognize the specific image features to prevent further unnecessary interventions. In addition, bone SPECT/CT could also make the diagnosis in one step.

1. Introduction

Osteopoikilosis is a rare benign bone dysplasia usually incidentally found on radiographs or computed tomography (CT) scans. Is it usually asymptomatic and characterized by multiple enostoses throughout the skeleton, but rarely there might be mild pain. Radionuclide bone scan plays a critical role in distinguishing from osteoblastic bone metastasis. It is important for clinicians to recognize the image patterns to avoid further unnecessary interventions.

2. Case presentation

A 37-year-old man without major medical history presented to orthopedic outpatient clinic with multiple joint pain especially at right hip for 2 weeks. Physical examination showed no limited range of motion nor focal inflammation sign. Pelvic X-ray film (Fig. 1) showed multiple discrete round radio-densities, known as bone islands, scattered throughout the pelvic bone, sacrum, lumbar spines, and bilateral proximal femur. To exclude osteoblastic bone metastases, whole-body Tc-99m methylene diphosphonate bone scintigraphy with pelvis single-photon emission tomography (SPECT)/CT regional scan was arranged. There was significant abnormal uptake (Fig. 2, panel A) on bone scintigraphy. Pelvic SPECT/CT (Fig. 2, panel B–G) of coronal and transverse views clearly revealed clusters of multiple, discrete, small punctuate, and hyperdense lesions without focal Tc-99m methylene diphosphonate-avid uptake throughout the pelvic bones and bilateral proximal femurs. Therefore, diagnosis of osteopoikilosis was made. The right hip discomfort then gradually subsided after supportive therapy including rest and oral nonsteroidal antiinflammatory drugs.

Figure 1.

Radiograph of pelvis showed multiple bone islands symmetrically distributed at the skeleton, primarily on pelvic bone, sacrum, and bilateral proximal femur.

Figure 2.

There was no obvious increased uptake on (A) whole body bone scan; however, (B–D) coronal and (E–F) transverse views of pelvis SPECT/CT showed numerous sclerosing lesions devoid of significant Tc-99m MDP avid uptake. CT ,computed tomography; MDP, methylene diphosphonate; SPECT, single-photon emission computerized tomography.

3. Discussion

First described in 1915 by Albers-Schonberg,^[1–2] osteopoikilosis is a benign bone condition with numerous sclerosing bone islands throughout the skeleton. It is a rare condition with incidence estimated around 1 in 50,000,^[3] and usually without age or gender differences.^[1] It is usually autosomal dominant in inheritance,^[1–6] but sporadic forms are also reported.^[1] The patients are usually asymptomatic and incidentally found with clusters of multiple enostoses predominantly on spongy cancellous bone on radiographs or CT scans, but up to 20% might complained of articular pain.^[1,2]

Current literatures suggest loss-of-function mutations of LEM domain containing 3 (LEMD3) gene located on 12q might be the cause, and the mutation could also affect soft tissue and skin, resulting in melorheostosis and Buschke–Ollendorff syndrome.^[7,8] A normal radionuclide bone scan excludes the possibility of osteoblastic bone metastasis.^[5] However, sometimes an abnormal bone scan, usually mild, could be seen, which reflects active osseous remodeling.^[4,6] Hybrid SPECT/CT images could be a good choice for differential diagnosis in unexplained bone pain in one step. Furthermore, it is important for clinicians to recognize the image presentations to avoid unnecessary examinations and treatments.