A solitary lytic rib lesion mimicking primary Chest Wall malignancy as the initial presentation of multiple myeloma

Abstract

Multiple myeloma is predominantly observed in the geriatric population and accounts for approximately 10% of all hematologic malignancies. It typically presents with multiple bone lesions and clinical features fulfilling the CRAB criteria (hyperCalcemia, Renal failure, Anemia, and Bone involvement). Herein, we present the case of an 82-year-old patient who presented with a solitary lytic rib lesion in the left hemithorax. The patient exhibited only bone pain among the CRAB features, and systemic radiological evaluation revealed no additional lesions. The initial clinical impression was that of a primary malignancy of the thoracic wall. A diagnosis of multiple myeloma was confirmed based on the histopathological evaluation of both the solitary lytic rib lesion and bone marrow samples.

Introduction

Chest wall masses arise from a broad etiologic spectrum, including tumors, infections, and inflammatory conditions. Management and prognosis rely on definitive histopathological diagnosis. Multiple myeloma (MM) is the second most common hematologic malignancy originating from plasma cells, characterized by the production of monoclonal immunoglobulins [1]. Although often presenting with nonspecific symptoms, MM causes destructive lytic lesions, osteoporosis, hypercalcemia, and other skeletal complications [2]. The ribs are frequent sites of metastasis from breast, prostate, lung, renal, and hematologic cancers, and rib lesions carry an extensive differential that includes primary chest wall neoplasms. Solitary rib tumors remain diagnostically challenging. This report describes an uncommon presentation of MM with an isolated lytic rib lesion mimicking a primary chest wall malignancy.

Case report

An 82-year-old male patient presented with aching pain over the left lateral chest wall at the ninth–tenth rib level, persistent at rest and partially responsive to analgesics. Trauma history, systemic symptoms, comorbidities, and relevant family history were absent. Physical examination revealed a mildly tender, palpable swelling at the left 9th posterior axillary line. Laboratory tests revealed hypochromic microcytic anemia with otherwise normal biochemical markers (Table 1).

Table 1.

Clinical, laboratory, and literature comparison data of the patient. Part a: Initial laboratory findings demonstrating monoclonal gammopathy and co-existing microcytic anemia due to the beta-thalassemia trait, without classic CRAB features (hypercalcemia or renal failure). Part B: Literature review of international cases presenting with solitary rib masses initially mimicking primary chest wall tumors, detailing their management strategies, histopathological diagnoses, and clinical outcomes in comparison to the current case.

Part A: current case laboratory data	Result			Reference range	Clinical significance
Hemoglobin/MCV	11.6 g/dL/66 fL			13.5–18/78–100	β-thalassemia trait
Calcium (Albumin-corrected)	9.2 mg/dL			8.8–10.6	No Hypercalcemia
Creatinine	0.69 mg/dL			<1.2	No Renal Failure
M-protein (Gamma region)	11.9 g/L (15.8%)			Negative	Monoclonal Gammopathy
Part B: literature comparison	Author (Year)	Age/Sex	Rib Level/Side	Initial Diagnosis	Management	Outcome/Progression
	Sharma (2016)	42/M	4th/Right	Primary rib tumor	Resection + Reconstruction	Diagnosed as MM post-op
	Citak (2025)	55.6 (range: 32–74 years)	Various (n = 6)	Solitary Plasmacytoma	Resection + Reconstruction	1 case developed distant metastasis
	Basavaiah (2019)	70/M	10th/Right	Solitary Plasmacytoma	FNAB for diagnosis + Radiotherapy	Local control achieved
	Current Case	82/M	9th/Left	Primary rib tumor	Systemic Therapy	Diagnosed with MM; lost to follow-up before treatment assessment

Abbreviations: MM: Multiple Myeloma, FNAB: Fine-Needle Aspiration Biopsy, MCV: Mean Corpuscular Volume, M: Male, F: Female, post-op: postoperative, f-up: follow-up.

Chest X-ray showed a pathological fracture and opacity at the left 9th lateral rib (Fig. 1). Non-contrast thoracic computed tomography (CT) revealed a mass measuring approximately 5.0 × 5.9 cm, causing bone destruction and extending into the subcutaneous tissue and adjacent muscle structures (Fig. 2). To evaluate possible systemic disease and detect additional lesions, on 18-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography/computed tomography (PET/CT), the lesion demonstrated a maximum standardized uptake value (SUVmax) of 4.40, with no evidence of pathological uptake elsewhere in the body (Figs. 3A–C). CT-guided fine-needle aspiration biopsy of the mass revealed a plasma cell neoplasm. On immunocytochemistry, these cells were CD38-positive (Fig. 4). Hemoglobin electrophoresis showed Hb A: 94.4% (reference range: 96.8%–97.8%), Hb F: 0.7% (normal ≤ 1.0%), and Hb A2: 4.9% (2.2%–3.2%), consistent with beta-thalassemia trait (Fig. 5A). Serum protein electrophoresis demonstrated a monoclonal spike in the gamma globulin region (M-protein: 11.9 g/l, 15.8%) (Fig. 5B). Serum immunofixation electrophoresis revealed elevated IgG lambda-type paraprotein. Bone marrow examination showed an increased number of CD138-positive plasma cells (30%), including morphologically immature forms, and confirmed lambda light chain monoclonality. Plasma cell ratio in aspiration smears was 10%–12%, with atypical forms observed. The patient was discussed at a multidisciplinary tumor board, and systemic therapy for multiple myeloma was recommended. However, the patient elected to continue treatment at another institution and was therefore lost to follow-up.

Figure 1.

Posterior- anterior chest X-ray showing a pathological fracture and opacity at the lateral aspect of the left ninth rib (arrow).

Figure 2.

Non-contrast thoracic CT demonstrating a lytic lesion in the left ninth rib associated with a hypodense surrounding soft tissue component (arrow).

Figure 3.

(A–C) ¹⁸F-FDG PET-CT showing FDG uptake in the left ninth rib (SUVmax: 4.40), with no evidence of additional organ or regional involvement (arrow).

Figure 4.

(A) Tumor composed of plasma cells diffusely infiltrating fibrous connective tissue (Hematoxylin & Eosin stain, ×200). (B) Diffuse, strong membranous CD38 staining in plasma cells on immunohistochemistry (×400).

Figure 5.

(A) Hemoglobin electrophoresis consistent with beta-thalassemia trait. (B) Serum protein electrophoresis showing a monoclonal M spike in the gamma-globulin region.

Discussion

Solitary rib masses encompass a broad differential diagnosis, including chondrosarcoma, metastatic carcinoma, Ewing sarcoma, and infections. In our patient, however, monoclonal gammopathy and bone marrow infiltration confirmed systemic Multiple Myeloma (MM) (Table 1). MM accounts for ~ 1% of cancers and 10% of hematologic malignancies [3], often diagnosed years after onset [1]. In newly diagnosed MM patients, the most common presenting features are anemia (73%), bone pain (58%), elevated creatinine (48%), fatigue (32%), hypercalcemia (28%), and weight loss (24%) [4]. Seesaghur et al. reported a median 220-day diagnostic delay from initial bone pain [2]. In our patient, the presence of beta-thalassemia trait, normal biochemistry, and isolated bone pain initially masked the diagnosis of MM.

MM typically presents with multiple osteolytic lesions involving the axial skeleton. In our case, the presence of a solitary bone lesion was not initially consistent with MM, and a PET/CT was therefore requested. Citak et al. observed varying FDG uptake (SUVmax: 3.8–11) in five of six solitary plasmacytoma cases [5]. The diagnostic sensitivity of 18F-FDG PET/CT in MM is limited due to tumor biology [6]. In our patient, FDG uptake was observed in the solitary bone lesion; however, in the absence of additional hypermetabolic lesions, primary chest wall neoplasms were considered in the differential diagnosis.

Sharma et al. reported the case of a 42-year-old male who presented with a lytic rib lesion [7]. Similarly, the initial findings were not suggestive of multiple myeloma. However, the diagnosis was established only after chest wall resection, and subsequent bone scintigraphy revealed additional skeletal involvement. In contrast, our patient underwent PET/CT during initial evaluation.

Solitary plasmacytoma (SP) comprises 2%–5% of plasma cell dyscrasias [8]. It is defined by localized monoclonal plasma cell proliferation without additional skeletal lesions, absence of CRAB features, and < 10% clonal plasma cells in the bone marrow [9]. Basavaiah et al. reported rib involvement in 3.4% of 29 patients [10]. Bone-based SP carries a > 60% risk of progression to MM, typically within 2–3 years [8]. In our patient, the absence of prior radiological imaging makes it uncertain whether the lesion represented progression from an undetected SP. While the initial radiological findings could suggest solitary plasmacytoma, bone marrow examination revealed 30% clonal plasma cells. According to the 2014 updated International Myeloma Working Group (IMWG) criteria, a diagnosis of MM is established when clonal bone marrow plasma cells are ≥10% or when a biopsy-proven plasmacytoma is present together with one or more myeloma-defining events (MDEs) [9]. In our patient, the 30% CD138-positive lambda-restricted plasma cell infiltration in the bone marrow clearly exceeded the diagnostic threshold, confirming multiple myeloma and differentiating it from solitary plasmacytoma.

The discrepancy between aspirate (10%–12%) and biopsy (30%) plasma cell percentages likely resulted from hemodilution and the patchy infiltration pattern characteristic of MM. In our case, the biopsy provided a more reliable assessment of tumor burden than the technically limited aspirate. Limitations of this report include restricted immunohistochemical evaluation of the chest wall lesion and lack of clinical follow-up, as the patient transferred to another institution, preventing assessment of long-term outcomes.

In conclusion, multiple myeloma in geriatric patients can present as isolated rib lesions, with bone pain as the only CRAB feature. The limited sensitivity of 18F-FDG PET/CT may mask systemic involvement. Clinicians should consider MM in the differential diagnosis of solitary rib masses, especially in elderly patients presenting with unexplained bone pain, and pursue minimum diagnostic steps, including laboratory evaluation, imaging, and biopsy, to avoid misdiagnosis and ensure timely management.

This study has not been presented in any meeting.

Conflicts of interest

All authors declare that there are no conflicts of interest or disclosures related to this manuscript.

Funding

This study was self-funded by the authors and received no external financial support from any funding organization.

Ethical approval

Not applicable.

Consent

Written informed consent was obtained from the patient for their anonymized information and accompanying images to be published in this article.

Guarantor

Corresponding author (Dr. İsmail Tombul).