A super scan is characterized by a strikingly high bone to soft tissue ratio on skeletal scintigraphy, with a uniform symmetrical increase in bone uptake and diminished to absent renal visualization ('absent kidney sign'). It can be seen in a variety of diseases in which there is diffusely increased bone turn over. Diffuse skeletal metastasis, as can be observed from primary tumors of the breast, lung, prostate, bladder and lymph nodes, is the most frequent cause. Other causes are secondary hyperparathyroidism, Paget disease, myelofibrosis and metabolic bone disease.
Technetium-99m-labeled methylene diphosphonate (99mTc-MPD) bone scintigraphy performed in patients presenting with prostate cancer shows metastases in 10–50%. It has a false negative rate of 1–5%, mostly being due to a super scan [1]. When caused by prostate cancer, super scans are found exclusively in histologically high-grade forms.
Hypertrophic Osteoarthropathy (HOA), also known as the classical Pierre Marie-Bamberger syndrome, is a systemic disorder of the bones, joints and soft tissues that develops in association with other disease processes. It is characterized by several or all of the following signs [2]: clubbing of the digits, periosteal new bone formation, particularly involving the long bones of the distal extremities, symmetric arthritis-like changes in the joints and periarticular tissues (ankles, knees, wrists, and elbows), increased thickness of the subcutaneous soft tissues in the distal one-third of the arms and legs and sometimes of the facial tissues, which may simulate acromegaly [3] and finally, neurovascular changes of the hands and feet including chronic erythema, paresthesia and increased sweating.
Most commonly it is associated with an intrathoracic malignancy, which can be carcinoma of the lung as well as pulmonary metastasis of other tumors and Hodgkin's disease involving the mediastinum. HOA is also frequently seen in severe cystic fibrosis, bronchiectasis, chronic empyema and lung abscess and occasionally in certain liver disorders' [4]. In some instances it may present without any underlying illness when it is called primary, idiopathic or the hereditary form of HOA in which bone and joint pain tends to be less, and the furrowing of the face and scalp tends to be more severe. Diagnosis must be based on global assessment of the clinical, laboratory and radiographic findings rather than the presence of one abnormality, since there are well-documented cases that lacked radiographically detectable periostitis [5]. Blood studies are usually unaffected by HOA except that often an elevated ESR of more than 50 mm/h is seen and in advanced cases an elevated alkaline phosphatase level can be found [6]. The incidence of clinically apparent HOA in patients diagnosed with lung cancer is approximately 4–5% [7]. The etiology is still poorly understood. Several pathogenetic theories have focused on the vascular changes and proliferation that might be caused by circulating growth factors that normally are inactivated in the lungs. Pulmonary shunting caused by the several disease processes that are associated with HOA causes a faulty pulmonary clearance of macrothrombocytes, which release growth factors in the systemic circulation. Elevated levels of platelet-derived growth factor (PDGF), endothelin-1 (ET-1), β-thromboglobulin (β-TG) and vascular endothelial growth factor (VEGF) [8] have all been shown to be elevated in patients with HOA.
HOA has no prognostic significance and early detection may lead to detection of potentially resectable lung carcinoma. Subclinical cases can be diagnosed by radiographs or, with more sensitivity, by skeletal scintigraphy with an incidence in bronchogenic carcinoma of up to 20% [6]. Usually scintigraphic abnormalities are found in the peripheral skeleton and are not easily mistaken for diffuse skeletal metastasis. Its appearance can range from increased 'bracelet-like' appearance to more diffusely increased uptake at the distal ends of the long bones. Although usually located in the peripheral skeleton, it can also affect the skull, claviculae, ribs and scapulae [9, 10]. Sometimes along the cortical margins, a 'parallel track sign' due to the periosteal bone formation can be seen. To the best of our knowledge this is the first report of a super scan as the presenting feature of HOA.
This case report clearly illustrates the pitfalls of diagnostic tests. The most important is the interpretation of the bone scan. Although the clinical presentation almost entirely fitted the suggested diagnosis of diffusely metastasized prostate carcinoma as an explanation for the symptoms, signs and bone scintigraphy, it was the normal PSA, which indicated that an alternative diagnosis should be sought. Studies report that a PSA of less than 20 ng/ml has a negative predictive value of 92–95% for the absence of skeletal metastases in patients with well-differentiated (grade 1 and 2) or clinically localized (stages T1–2) prostate cancer. In patients with poorly differentiated (grade 3) or clinically advanced (stages T3–4) tumors it has a negative predictive value of only 70 and 50%, respectively [10, 11]. And although advanced technologies are at our disposal, in almost 4.5 liters of pleural fluid no malignant cells were found. Imaging technologies are so refined that peripheral embolism on a CTA can be detected, but gross abnormalities like pleural fluid and atelectasis can cover up a malignant tumor of 10 cm in diameter.
