POEMS syndrome is a rare condition with the acronym representing some (but not all) key paraneoplastic features of the syndrome: polyneuropathy, organomegaly, endocrinopathy, monoclonal plasma cell disorder, and skin abnormalities. There are established diagnostic criteria with the mandatory ones being polyneuropathy and a monoclonal plasma cell disorder [1]. In addition, one of three major criteria and one of six minor criteria are required to secure the diagnosis [1]. In this case, the solitary plasmacytoma serves as one of the mandatory criteria, despite the absence of systemic multiple myeloma [1]. The co-diagnosis of Castleman’s disease and a sclerotic bone lesion serves as major criteria. Bone lesion, if present in POEMS syndrome, is characteristically sclerotic [2], in contrast with solitary plasmacytoma without POEMS that is typically a purely lytic lesion. She also has a plethora of minor criteria conditions, characterized by splenomegaly (organomegaly), diabetes (endocrinopathy), thrombocytosis with prior thrombotic disease, papilledema, and edema. However she did not have characteristic features of skin changes such as hyperpigmentation or acrocyanosis [3] nor pulmonary manifestations [4]. Patients with POEMS syndrome have these disparate symptoms and signs, and it is quite common to have some typical features but not others, which is the reason why it is difficult to diagnose, in addition to its rarity (prevalence <0.5 per 100,000). Delays in establishing a diagnosis is unfortunately common with median time from onset of symptoms to diagnosis of 19 months in a series of 38 patients [5], similar to that observed in this case. The pathogenesis of POEMS is poorly understood, but it is known that treating the underlying monoclonal plasma cell disorder can result in improvement of the syndrome [1, 6, 7]. There is no documentation of IgA nephropathy to be associated with development of POEMS or plasma cell diseases, although one can speculate whether the immunosuppression might have a role in her developing the plasma cell neoplasia. It appears that elevated VEGF levels reflect the disease activity, but anti-VEGF therapy alone has not been successful suggesting that it is another manifestation of the disease rather than having a causative role [1].

The workup of a suspected diagnosis of solitary plasmacytoma is directed to exclude multiple myeloma. The following criteria must be satisfied: a biopsy-confirmed single lesion with negative skeletal imaging elsewhere, normal bone marrow biopsy (<10 % clonal plasma cells), and no myeloma-related organ dysfunction (normal blood counts, calcium and renal function) [8, 9]. A monoclonal protein can be present in blood or urine, but it is usually only minimally elevated. Solitary plasmacytomas present more commonly in the bone, and usual symptoms are pain, neurologic compromise (e.g., from vertebral lesion causing nerve or spinal cord compression), and sometimes pathologic fracture. It is unusual to be locally asymptomatic as in this case with the scapula lesion. Solitary plasmacytoma uncommonly presents in an extramedullary site (20 %), usually as a soft tissue mass in the head and neck areas [10]. After adequate local treatment, it is known that an extramedullary presentation is associated with a lesser probability of progression to multiple myeloma [10], in contrast with a bone presentation where the disease recurs as multiple myeloma with a high likelihood, usually within 5–10 years [9, 11].

When the patient was assessed for radiation therapy, she was severely disabled and totally bedridden (ECOG performance status 4) due to her neuropathy and generalized edema. She required frequent care in hospital, and have not experienced any improvement following multiple pulse treatments with high-dose glucocorticoids and intravenous immunoglobulin treatment. It was elected to treat her with radiation therapy to the right scapula lesion, her only documented plasmacytoma. She received 35 Gy in 15 fractions (2.33 Gy fractions) over 3 weeks. This shorter regimen was chosen as she required inter-hospital transfer daily for her RT. Other acceptable regimens in common use are 40–45 Gy in conventional fractionation. However one of the largest multi-institutional reviews showed no evidence of dose response beyond 30 Gy in terms of local control, regardless of size of the tumor [11]. A 3D conformal treatment plan was used choosing beam angles and segmental fields to minimize lung exposure (Figs. 6.4 and 6.5). She tolerated RT well and was transferred to a rehabilitation facility following completion of radiation. At 6 months follow-up, she improved neurologically with recovery in her arms, but still unable to walk. Her edema resolved. Her serum VEGF level returned to normal. Repeat FDG PET/CT scan showed improvement in the scapula lesion, SUVmax decreased to 10.7 and no new lesions detected. Repeat bone marrow biopsy remained negative. One year following RT, she started to ambulate and was able to be discharged home. Repeat FDG PET/CT scans 16 months and 21 months post-RT showed complete metabolic response (no visual uptake in the right scapula), although CT scan continues to show some residual sclerosis at the local site. The patient functioned well apart from residual mild leg weakness.

Four years after RT, she experienced some worsening of her motor strength, and investigations revealed a recurrence of her POEMS syndrome with multiple FDG PET-avid spinal sclerotic lesions (Fig. 6.6) which were new, although small and asymptomatic. The scapula lesion remained controlled with no FDG uptake. She had elevation of serum VEGF (875 pg/ml). However her bone marrow biopsy remained negative for multiple myeloma, and she maintained absence of M-protein in blood and urine. After a brief course of chemotherapy with oral cyclophosphamide and prednisone, she received an autologous peripheral blood stem cell transplant with conditioning regimen consisting of melphalan 200 mg/M² and tolerated it well. Her further follow-up is awaited.