Kappa Light Chain Deposition Disease Presenting with Axonal Sensorimotor Polyneuropathy in the Absence of Clinically Significant Renal Pathology
Background:
Light chain deposition disease (LCDD) is a non-fibrillar, non-amyloid monoclonal light chain (usually kappa) disorder. LCDD nearly always manifests with nephropathy, usually in the form of glomerulosclerosis with nephrotic range proteinuria. Approximately 35% of patients have extra-renal lesions, typically involving the liver, nervous system, or myocardium, but are rarely symptomatic. Peripheral neuropathy secondary to LCDD has rarely been described, and to our knowledge, neuropathy as the predominant clinical manifestation has never been described. We present a case of kappa LCDD presenting with axonal sensorimotor polyneuropathy in the absence of clinically significant renal pathology.
Results:
An 86-year-old man presented with one year of insidiously progressive numbness of the hands and feet, gait imbalance, and impaired hand dexterity. His exam was notable for length-dependent multimodal sensory loss, mild distal limb weakness, diminished reflexes, and sensory ataxic gait. Electrodiagnostic testing showed severe, chronic, length-dependent axonal sensorimotor polyneuropathy with active denervation of the distal lower extremity as well as severe median neuropathy at both wrists. Laboratory evaluation revealed elevated serum and urine kappa light chains (κLC) with evidence of monoclonal κLC production by urine immunofixation. Subsequent bone marrow biopsy showed kappa restricted clonal plasmacytosis. Immunohistochemical staining for κLC of an abdominal fat pad specimen was negative, but an endomyocardial biopsy, pursued due to mildly reduced ejection fraction, low-voltage EKG, and abnormal cardiac MRI, was positive. He was treated with daratumumab and dexamethasone with gradual reduction in serum and urine κLC concentrations and partial improvement in his neuropathy.
Conclusions:
While nephropathy is classically ubiquitous in LCDD, clinically significant extra-renal manifestations are possible in its absence, as we herein report a case of severe and progressive axonal sensorimotor polyneuropathy due to LCDD that was partially responsive to chemotherapy. Diagnosis of LCDD requires a high-index of suspicion as pathologic investigation must specifically include κLC immunohistochemistry.