Other differential diagnoses were considered in this patient. Nonsteroidal anti-inflammatory drugs and analgesic drugs can cause acute kidney injury or acute interstitial nephritis, especially with long-term use or in individuals with preexisting renal impairment, in whom the risk may be as high as 20%. In this case, that diagnosis would not explain the presence of significant and worsening low back pain, hypercalcemia, or markedly elevated ESR. In addition, leukocytes in the urine would probably be present.
Tuberculous spondylitis (Pott disease) is rare in the general population in the United States. Approximately 9000 cases are diagnosed each year, most commonly in persons not born in the United States and in immunocompromised patients with HIV/AIDS, steroid use, chronic liver disease, or uncontrolled diabetes. Minimal local findings are observed in Pott disease until it advances and spinal deformity develops. Although elevated ESR and mild anemia are common features, that diagnosis would not explain the elevated serum creatinine and calcium levels that were noted in this patient.
Primary paraspinal pyomyositis is rare in the United States. Unlike tuberculosis, it is an acute infection that occurs over the course of several weeks, with persistent fevers and findings of local paraspinal edema, warmth, and tenderness upon examination. In addition to an elevated ESR, neutrophil leukocytosis with toxic granulation is expected. Anemia and hypercalcemia are not characteristic of this condition. In addition, the patient's spinal MRI findings were not consistent with any of the three differential diagnoses and excluded the presence of spinal cord compression or any paraspinal mass.
MM is a plasma cell cancer first described in 1848. Over 30,000 patients in the United States are diagnosed with MM each year. It is the second most common hematologic cancer in adults, accounting for 10%-20% of the total and 1% of adult cancers overall. The clinical spectrum of MM ranges from monoclonal gammopathy of unknown significance (MGUS) to plasma cell leukemia.
"MGUS" refers to the presence of monoclonal immunoglobulins on SPEP in the absence of any evidence of MM. The term arose because the condition is often an incidental finding, and the condition may remain benign for many years. MGUS affects 3% of apparently healthy patients older than 50 years. Certain laboratory findings should lead to caution in a diagnosis of MGUS, including the following:
M component level > 3 g/dL or rising
Spleen and liver involvement
Marrow plasma cells > 10%
Presence of light chains in the serum or urine
Over a period of 20 years, 25% of such patients progress to cancer. The presence of any of these factors can dramatically increase the likelihood of malignancy. Primary amyloid light chain amyloidosis is a rare disease found in 15%-20% of patients with MM. Insoluble monoclonal immunoglobulin light chains or fragments are deposited in tissues. Clinical manifestations are protean and often lead to early death due to heart failure or renal failure (nephrotic syndrome).
Imaging for bony lesions is an important part of diagnosis. In this case, radiography was misleading. Whole-body X-ray (WBXR) has a false-negative rate of 30%-70% in MM, and lack of bone abnormalities does not exclude diagnosis. WBXR also does not detect diffuse bone marrow involvement, and osteopenia due to MM cannot be distinguished from senile and postmenopausal osteoporosis. The IMWG recommends that patients with possible MM be screened for skeletal lesions using low-dose CT, whole-body PET/CT, or MRI. Technetium-99 bone scans are unhelpful in MM, because osteoblastic repair activity is minimal.
Clinically, patients are at risk for pathologic fractures and may develop neurologic complications or symptomatic hypercalcemia. Urgent assessment with MRI of the spine is needed if vertebral collapse or clinical signs of cord compression are noted.
Imaging does not currently play a role in staging. Staging includes a three-tier International Staging System (ISS), which regards low beta2-microglobulin level and normal serum albumin as favorable factors. Around half of patients with MM have translocations that involve the immunoglobulin heavy-chain locus on chromosome 14q32. Revised ISS (R-ISS) staging uses unfavorable cytogenetics to define high risk, including del(17p), t(4;14), or t(14;16) and elevated serum lactate dehydrogenase (LDH) level.[4,17] The patient in this case was classified as stage II on ISS and lacked high-risk cytogenetics and an elevated LDH level. Thus, he was placed in an intermediate-risk category.
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