Neuro-Myelomatosis of the Brachial Plexus – An Unusual Site of Disease Visualized by Fluorodeoxyglucose-Positron Emission Tomography/Computed Tomography (FDG-PET/CT): A Case Report

Background

Neurologic manifestations often complicate the course of patients with multiple myeloma (MM) and the peripheral neuropathies are usually related to amyloidosis or compression by tumors [1]. The pathogenesis of extramedullary involvement in MM is speculated to be as follows: 1) direct extension from MM skeletal lesions with disruption of the cortical bone; or 2) hematogenous metastatic spread to any tissue or organ, the most frequent being the skin, liver, kidney, or central nervous system [2]. The reported incidence of extramedullary involvement in newly diagnosed MM ranges from 7% to 18% [3]. Although several imaging techniques can aid in the assessment of extramedullary involvement in MM, the International Myeloma Working Group published a consensus statement indicating that PET/CT imaging should be performed in all patients in whom extramedullary involvement is suspected [4].

Here, we present a case of neuro-myelomatosis of the brachial plexus diagnosed using 18F-FDG PET/CT. To the best of our knowledge, it is the first documented case of neuro-myelomatosis of the brachial plexus.

Case Report

A 63-year-old Japanese woman visited a general practitioner with chief complaints of right shoulder and upper extremity pain. Although the patient’s physical examination was unremarkable, the transverse T2-weighted MRI images (T2WI) of head and neck (Figure 1A) and fat-saturated T2WI (Figure 1B) revealed a mild, high-intensity lesion along the right brachial plexus. Coronal gadolinium-enhanced T1-weighted images (Figure 1C) revealed mild, diffuse contrast-enhancement in the lesion, which is a non-specific signal pattern of brachial plexus lesions such as metastatic tumors, benign neurogenic tumors, malignant nerve sheath tumors, and Ewing sarcomas [5].

One week after the MRI findings, the patient presented with unexpected thrombocytopenia (3.2×104/μL), high serum level of LDH (16320 U/L), and IgD (197 mg/dL). Then, the serum immunoelectrophoresis and bone marrow biopsy were quickly performed for advanced diagnostic purposes. These results were as follows: M-protein of the IgD-lambda type, and infiltration of clonal plasma cells with CD3 (−), CD4 (−), CD7 (+), CD10 (−), CD20 (−), CD38(+), CD56 (−), CD138 (−), Bcl-2 (−), Bcl-6 (−), c-Myc (+), MUM-1 (+), PAX5(−), OCT2(+), bob1(+), kappa(−) and lambda(+). Thus, physicians strongly suspected MM from the patient’s clinical characteristics.

As shown in Figure 2, The 18F-FDG PET/CT fusion images and maximum intensity projections of her whole-body scan revealed high-intensity FDG uptake in multiple intramedullary lesions [6], and similar uptake was observed along the right brachial plexus, where the mass lesion had been detected previously via MRI. The 18F-FDG PET/CT images revealed neither disruption of cortical bone adjacent to the medullary lesions nor remodeling/destruction of trabecular bone, consistent with neuro-myelomatosis of the brachial plexus, which is defined as extramedullary neural involvement associated with MM.

The neuropathic pain was improved with high-dose dexamethasone therapy. In addition, after the combination chemotherapy with etoposide, prednisolone, vincristine, Adriamycin, and cyclophosphamide, the plasma cells in the bone marrow almost disappeared. The 18F-FDG PET/CT images confirmed complete metabolic remission of the intramedullary lesions and the right brachial plexus lesion.

Discussion

One of the clinical features of IgD MM is the common occur-rence of cytogenetic abnormalities as well as extramedullary involvement [7]; thus, this condition may present with variable symptoms caused by the invasion of a variety of organs, including neuro-myelomatosis. Although neurological manifestations frequently complicate the course of patients with MM [8], peripheral neuropathy is also a common complication of many of the systemic amyloidoses [9]. Neuropathies related with neuro-myelomatosis are treatable pathological conditions; therefore, differentiating neuro-myelomatosis from neuro-amyloidosis is of clinical importance.

Conclusions

Although neuro-myelomatosis are difficult to diagnose, this case establishes 18F-FDG PET/CT as a potentially useful imaging modality for the diagnosis of extramedullary lesions associated with MM.