Japanese Journal of Clinical Oncology

DISCUSSION

Compared with solitary plasmacytoma of the skull base, the prognosis for solitary plasmacytoma of the skull vault seems to be good when there is no evidence of systemic myelomatosis. Nevertheless, solitary plasmacytoma of the skull vault also has a possibility of being identical with SPB. SPB has been defined by Woodruff et al. (4) as a solitary osteolytic lesion without evidence of MM on bone marrow examination. True SPS is much rarer than SPB and only 35 cases have been reported in the English literature (Table 1) (2,3,5-23).

Table 1. Solitary plasmacytoma of the skull

Series (Ref. No.)	Age (yr), sex of patients	Location	XRT	Follow-up interval (months)	Multiple myeloma
Mathias (1935) (5)	65, M	Parietal	-	?	?
Kaufman (1945) (6)	14, M	Rt occipital	1755 r	120	-
Moossy (1967) (7)	44, F	Lt frontal	+	54	-
Chang (1970) (8)	47, M	Rt parietal	+	36	-
Kutcher (1974) (9)	51, M	Lt parietal	30 Gy	24	-
Corwin (1979) (10)	71, M	Rt parietal	40 Gy	24	-
Jakubowski (1980) (2)	17, M	Lt occipital	+	84	+
	47, M	Rt parietooccipital	+	24	-
	60, M	Mid parietal	+	6	+
	40, M	Rt parietal	+	12	+
	38, M	Rt occipital	+	8	-
Soffer (1982) (11)	61, F	Lt parietal	40 Gy	12	-
Mancardi (1983) (12)	62, M	Skull base	45 Gy	19	-
Arienta (1987) (13)	37, F	Parietal	-	?	-
	64, F	Parietal	-	?	-
Du Preez (1991) (14)	30, F	Rt frontotemporal	-	18	-
	52, F	Rt frontal	-	16	+
Marais (1992) (15)	64, M	Skull base	44 Gy	18	-
Anonymous (1992) (16)	65, M	Skull base	-	?	?
Salvati (1994) (18)	68, F	Rt parietal	50 Gy	156	-
George (1994) (17)	47, M	Rt temporal	+	?	?
Prasad (1994) (19)	24, M	Rt parietal	40 Gy	15	-
	24, M	Lt temporal	40 Gy	14	-
Kuzeyli (1995) (21)	43, M	Lt frontal	-	?	?
Shih (1995) (22)	33, F	Skull	-	79	+
	21, F	Skull	-	87	-
	40, M	Skull	50 Gy	48	-
	40, M	Skull	50 Gy	30	-
Bindal (1995) (20)	51, F	Skull base	50 Gy	96	+
	51, F	Lt parietal	50 Gy	24	-
	30, M	Skull base	45 Gy	3	+
	47, M	Rt parietal	50 Gy	300	-
	75, M	Lt occipital	45 Gy	48	+
Matsuda (1996) (3)	55, F	Rt temporal	50 Gy	24	-
Okamoto (1997) (23)	72, F	Rt occipital	?	48	-

XRT = radiation therapy; ? = unknown; r = roentgen unit.

Table 2. Risk grouping of MM (33)

Risk group	Criterion	Median survival (months)
Low	PCLI < 1% and [beta]2M < 2.7 mg/l	71
Intermediate	PCLI [ge] 1% or [beta]2M [ge] 2.7 mg/l	40
High	PCLI [ge] 1% and [beta]2M [ge] 2.7 mg/l	17

PCLI = plasma cell labeling index; MM = multiple myeloma, b₂M = b₂-microglobulin.

CT shows an osteolytic lesion without a sclerotic rim, a hyperdense tumor and homogeneous postcontrast enhancement (2,15,16,19,20). The MR appearance is either isointense, hyperintense or heterogeneous intensity compared with the brain parenchyma on T₁-weighted images and homogeneous enhancement by intravenous administration of Gd-DTPA (15,17,19,20,23,24). Osteolytic lesion can usually be identified on X-ray film (14). The sharp borders, the lack of bony sclerosis and the paucity of periosteal reaction are characteristic findings of solitary plasmacytoma (23,25).

Surgical removal followed by postoperative irradiation is the treatment of choice because SPB is very radiosensitive (14,20). High local control rates are reported with radiotherapy, although the optimum dose and extent of radiotherapy portals remain controversial (7,10,26). The local tumor recurrence rate is less than 10% by conventional radiotherapy (24). The efficacy of chemotherapy for SPB, however, is not certain. Shih et al. (22) and Delauche-Cavallier et al. (27) failed to find any benefit on the outcome for patients who had received chemotherapy.

The diagnosis of SPB is based on a radiologically solitary bone lesion, plasma cells in the biopsy specimen, fewer than 5% plasma cells in bone marrow, less than 2.0 g/dl monoclonal protein (M-protein) in the serum when present, negative urine test for Bence Jones protein, no evidence of hyperglobulinemia and hypercalcemia and absence of anemia (7,24). On the other hand, the minimum criterion for the diagnosis of MM is the existence of more than 10% plasma cells in the bone marrow or that for plasmacytoma plus one of the following: (1) M-protein in the serum (usually 3.0 g/dl), (2) M-protein in the urine and (3) osteolytic lesion (28).

Bone marrow involvement in MM is patchy and the specimen may be taken from a region not involved with the disease. Skeletal survey is also insufficient for the precise diagnosis of SPB. A recent report by Moulopoulos et al. (29) indicated that MR imaging showed additional bone abnormalities which had not been detected by standard skeletal survey in some patients with a diagnosis of SPB. The amount of M-protein is not a precise prognostic factor of SPB while persistence of an M-protein after radiotherapy was a predictor of subsequent development of MM (24,30,31). Discrimination of SPB from MM is especially difficult because there is only a small difference in data for diagnosis such as number of plasma cells in bone marrow, amount of M-protein in serum and single or multiple osteolytic lesions. Hence it is necessary to make regular follow-up examinations for myelomatosis.

On the other hand, it is very useful to know which patients with SPB are at risk of developing MM at presentation. Several authors have tried to determine which factors may influence the prognosis of patients with MM (32,33). Greipp et al. (33) concluded that NPCLI using BrdU labeling and [beta]₂M measured at diagnosis were independent prognostic factors and the combination of NPCLI and [beta]₂M provides a more accurate assessment of survival probability than could be obtained with clinical staging (Table 2). The median NPCLI was 0.2% for patients with benign monoclonal gammopathy, 0.8% for patients with new, untreated MM and 1.7% for patients with MM in relapse (1,24). Serum [beta]₂M levels are increased in several benign conditions such as chronic inflammation, liver disease, renal dysfunction and some acute viral infections. Increased levels of [beta]₂M have also been found in a variety of malignancies, especially hematological malignancies. A large Southwest Oncology Group (SWOG) study involving over 600 patients supports the utility of serum [beta]₂M values as a prognostic factor for survival in multiple myeloma (34). Aviles et al. (35) reported that [beta]₂M is also the most powerful prognostic factor in patients with plasma cell dyscrasias. We believe that the determination of [beta]₂M should be included in the clinical evaluation of patients with solitary plasmacytoma.

Of course, this risk grouping in MM is still inadequate for the detection of the optimum therapeutic procedure for an individual patient. However, it is significant to apply this risk grouping to SPS, which is too rare to determine prognostic factors. According to this grouping, the present case is at risk of developing MM not according to standard clinical features but to a high NPCLI of 0.8%.