Kappa light chain--myeloma associated with adult Fanconi syndrome: response of the nephropathy to treatment of myeloma

A case of Fanconi syndrome accompanied by crystal depositions in tubular cells in a patient with multiple myeloma

Fanconi syndrome (FS) is a rare condition that is characterized by defects in the proximal tubular function. A 48-year-old woman was admitted for evaluation of proteinuria. The patient showed normal anion gap acidosis, normoglycemic glycosuria, hypophosphatemia, and hypouricemia. Thus, her condition was compatible with FS. The M peak was found behind the beta globulin region in urine protein electrophoresis. Upon bone marrow examination, we found that 24% of cells were CD138+ plasma cells with kappa restriction. From a kidney biopsy, we found crystalline inclusions within proximal tubular epithelial cells. Thereafter, she was diagnosed with FS accompanied by multiple myeloma. The patient received chemotherapy and autologous stem cell transplantation, and obtained very good partial hematologic response. However, proximal tubular dysfunction was persistent until 1 year after autologous stem cell transplantation. In short, we report a case of FS accompanied by multiple myeloma, demonstrating crystalline inclusion in proximal tubular cells on kidney biopsy.

Adult Fanconi syndrome secondary to light chain gammopathy. Clinicopathologic heterogeneity and unusual features in 11 patients

Fifty-seven cases of Ig light chain-associated Fanconi syndrome (FS) have been reported so far, mostly as isolated reports. The pioneering work by Maldonado and associates (35), who reviewed the first 17 cases in 1975, led to the unifying concept that patients with FS and Bence Jones proteinuria have a special form of plasma cell dyscrasia characterized by slow progression of the tumor and by prominent crystal formation in proximal tubule cells, in the absence of myeloma casts in the distal tubule. We carefully reappraised these characteristics in a series of 11 patients. Ten renal biopsy specimens were available for electron microscopy, adding to the 15 previously reported cases with ultrastructural studies. Moreover, 10 of the kappa light chains could be entirely or partially sequenced and tested for their resistance to cathepsin B, a lysosomal protease present in proximal tubule cells. Our series showed an unexpected clinicopathologic heterogeneity. Seven patients presented with the typical clinical and pathologic features of FS and low-mass myeloma or monoclonal gammopathy of undetermined significance (MGUS), in keeping with Maldonado et al's description. Crystals in bone marrow cells were detected in patients of this group, only. Three patients who presented with full-blown FS exhibited, however, the characteristic features of myeloma cast nephropathy in the setting of high-mass myeloma. One patient of this group also had numerous crystals in proximal tubule cells. The eleventh patient had complete FS with MGUS, but no crystals in proximal tubule cells even after electron microscopy. Contrasting with the clinicopathologic heterogeneity, genetic and biochemical analyses of the light chains showed a striking homogeneity. First, they all were of the kappa type. Second, 8 of 9 belonged to the V kappa I variability subgroup, which indicates that FS light chains are related by the sequence of their variable regions. Third, the 8 V kappa I light chain sequences most likely originated from only 2 germline genes, LCO2/012 and LCO8/018. Fourth, all 5 LCO2/012-derived sequences presented an unusual hydrophobic or nonpolar residue at position 30. These sequence peculiarities may account for unusual physicochemical properties of the light chains including the resistance of their variable domain V kappa to proteolysis by cathepsin B, observed in 7 of 9 patients in our series, while light chains isolated from patients with myeloma cast nephropathy are completely digested. Resistance of V kappa to proteolysis in FS patients can explain the accumulation of the light chain in the endocytotic compartment of the proximal tubule cells, leading to impairment of proximal tubule functions.

Acquired Fanconi's syndrome associated with monoclonal gammopathies

Franconi's syndrome is a rare complication of the monoclonal gammopathies characterized by diffuse failure in reabsorption at the level of the proximal renal tubule resulting in glycosuria, generalized aminoaciduria, and hypophosphatemia. Current evidence suggests monoclonal light chains that are incompletely digested in renal tubule lysosomes cause renal injury. The light-chain fragments serve as a nidus for crystal formation, and the crystals interfere with a broad range of apical membrane transporters. Franconi's syndrome is predominantly associated with monoclonal kappa in the urine, but rare instances of FS caused by lambda light chains have been described. Overt hematologic malignancies such as multiple myeloma, Waldenström's macroglobulinemia, or other lymphoproliferative disorders occur in one third of patients. Clinical manifestations include slowly progressive renal failure and bone pain caused by osteomalacia. The osteomalacia is caused by chronic hypophosphatemia and may be exacerbated by secondary hyperparathyroidism and renal tubular acidosis. Treatment consists of supplementation with phosphorus, calcium, and vitamin D. The osteomalacia is often completely reversible with mineral supplementation. Patients with an associated symptomatic malignancy or rapidly progressive renal failure may also benefit from chemotherapy. The prognosis is good in the absence of overt malignant disease.

Osteomalacia associated with adult Fanconi's syndrome: clinical and diagnostic features

OBJECTIVE

Osteomalacia associated with adult acquired Fanconi's syndrome is thought to result from hypophosphataemia and relative 1,25-dihydroxyvitamin D deficiency. We have followed the clinical and diagnostic features of patients with osteomalacia associated with adult Fanconi's syndrome, with particular emphasis on their responses to treatment with calcium, phosphate and vitamin D.

DESIGN

Retrospective Mayo Clinic case-note review from 1975 to 1994 and prospective follow-up study, combined with literature review.

PATIENTS

Eleven patients (7 male, 4 female) were identified who satisfied criteria for diagnosis of osteomalacia and adult Fanconi's syndrome. Twenty-five additional patients were identified in a literature review from 1954 to the present.

METHODS

Clinical history and physical examination, serum and urine bone and mineral parameter, X-ray radiography and iliac crest bone histomorphometry.

RESULTS

All patients presented with typical symptoms of osteomalacia, including lower extremity or low back bone pain, and all had fractures, pseudofractures, and/or bone demineralization on X-ray radiography. Osteomalacia and Fanconi's syndrome were diagnosed concurrently in 10 patients, whereas osteomalacia preceded diagnosis of Fanconi's syndrome by 5 years in one patient. Pre-treatment bone biopsies in 9 of the 11 patients demonstrated increased osteoid surface, volume and width. In the one patient labelled with tetracycline prior to biopsy, mineralization lag time was prolonged at 111 days (normal 19.2 +/- 1.0 days). Hypophosphataemia, inappropriately low 1,25-dihydroxyvitamin D levels, renal insufficiency, and chronic acidosis due to bicarbonate leak and uraemia, contributed to the osteomalacia in these patients. Secondary hyperparathyroidism was present in two patients. Eight of the 11 patients with osteomalacia associated with Fanconi's syndrome had monoclonal disorders, including multiple myeloma or lymphoma, many of them manifest by light-chain proteinuria. Over a mean patient follow-up period of 46 months (range 1-239 months), patients responded symptomatically to calcium, phosphate, and vitamin D replacement typically within 1-6 months. In 8 patients in whom follow-up data were available, post-treatment serum phosphate and 1,25-dihydroxyvitamin D levels improved in the setting of stable mild renal insufficiency; only one patient developed end-stage renal failure after 20 years, suggesting that these patients do not invariably progress rapidly to renal failure.

CONCLUSIONS

Regardless of the underlying cause, osteomalacia associated with adult acquired Fanconi's syndrome appears to respond well to calcium, phosphate, and vitamin D replacement. These patients do not appear to necessarily require 1,25-dihydroxyvitamin D replacement.

Monoclonal proteins and renal disease

Renal insufficiency, which is present initially in almost half of patients with multiple myeloma, usually results from myeloma kidney or hypercalcemia. Neither the class of light chain nor the isoelectric point plays an important role in kidney failure. Acute renal failure must be treated with appropriate fluids and with electrolytes and hemodialysis if necessary. Plasma exchange may be helpful, but has not been proven as such. The presence of a nephrotic syndrome and a monoclonal kappa or lambda light chain in the urine almost always indicates primary amyloidosis (AL) or light-chain deposition disease. Amyloid fibrils must be distinguished from the fibrils of immunotactoid glomerulopathy.

Plasma cell dyscrasias: current status

This is a review of the current status of the monoclonal gammopathies (plasma cell dyscrasias). We begin with the recognition of a monoclonal protein in serum and urine. We briefly discuss the differential diagnosis of the monoclonal gammopathies. Clinical and laboratory findings as well as the management of multiple myeloma are addressed. Future approaches for the treatment of myeloma are provided. The variant forms of multiple myeloma, including smoldering myeloma, plasma cell leukemia, nonsecretory myeloma, IgD myeloma, osteosclerotic myeloma, solitary plasmacytoma of bone, and extramedullary plasmacytoma, are briefly reviewed. Diagnosis and treatment of Waldenström's macroglobulinemia are presented. The recognition and differential diagnosis of the heavy-chain diseases (gamma, alpha, and mu) are included. Monoclonal gammopathy of undetermined significance ("benign" monoclonal gammopathy) is presented in detail. Amyloidosis is not included in this review.

Adult Fanconi syndrome progressing to multiple myeloma

A case of adult Fanconi syndrome is described in which there was urinary excretion of kappa light chains. After 13 years the patient developed overt myeloma. She also developed an adenocarcinoma of the colon and an adenocarcinoma of the parathyroid gland. These findings are discussed in relation to the known association between adult Fanconi syndrome, renal damage, and myeloma.

Renal lesions in multiple myeloma: their relationship to associated protein abnormalities

Renal biopsy and autopsy specimens were studied in 43 patients with renal complications of multiple myeloma and correlated with immunoelectrophoresis (IEP) and other clinical data at the time of biopsy. Lesions specifically related to multiple myeloma fell into two categories, with different patterns of protein excretion. (1) Myeloma Cast Formation: When other lesions which might contribute to renal insufficiency (RI) were excluded, there was a good correlation between the extent of myeloma cast formation and severity of RI. Sixteen of 19 patients excreted free light chains (LCs) in the urine, in seven as the predominant or sole urinary protein. (2) Tissue Deposition of Paraproteins: Nine cases had generalized glomerular, tubular basement membrane and vascular deposits of presumed kappa-chains (one with associated alpha-heavy chains). Four patients, all with myelomas secreting lambda LCs, had diffuse amyloid deposits in similar distribution. All patients (save two who were anuric) had diffuse, nonselective proteinuria by IEP, most within the nephrotic range. Four patients had free LCs in the urine, but in none was this the predominant component. Cast nephropathy and LC tissue deposition tended to occur in mutually exclusive fashion. Cases with diffuse tissue deposits of LCs showed few or no myeloma casts. Cases with cast nephropathy had only occasional mild mesangial lesions and focal interstitial and vascular deposits of amyloid. Evidence indicates that these lesions represent incidental LC deposition in cases whose basic lesion is longstanding and/or severe cast nephropathy, and that their contribution to RI is minor in comparison to that of the myeloma casts.

Unique amino acid sequences of Bence Jones proteins in the urine of patients with adult Fanconi syndrome

The amino-terminal amino acid sequences of Bence Jones (BJ) proteins isolated from the urine specimens of two patients (JBL and PSM) with adult Fanconi syndrome were determined. Both BJ proteins JBL and PSM are of the VkI subclass. However, protein JBL contains tyrosine at position 14 whereas protein PSM contains glutamine at position 40. Neither tyrosine 14 nor glutamine 40 has previously been reported for immunoglobulin (Ig) L-chains of any species including humans, the mouse, rabbit, rat, guinea pig. pig, dog, chicken, turkey, and shark. In addition, protein JBL contains alanine 22 whereas protein PSM contains arginine 30. Both alanine 22 and arginine 30 have been only rarely found in Ig L-chains.