A Curious Case of Leg Swelling With Eosinophilic Fasciitis, IgA-κ Monoclonal Gammopathy, Proteinuria, and Bilateral Carpal Tunnel Neuropathy: Diagnostic Convergence of Sclerosing Dermato-Fasciitis and Monoclonal Gammopathy.

Eosinophilic fasciitis (EF) is a rare sclerosing disorder characterized by limb edema evolving to woody induration with peau d'orange texture and the groove sign. Diagnosis typically requires a full-thickness fascial biopsy, while magnetic resonance imaging (MRI) can noninvasively demonstrate fascial thickening and guide biopsy. EF has recognized associations with hematologic conditions, including monoclonal gammopathy. A previously healthy 64-year-old woman developed progressive lower extremity hyperpigmentation, edema, and painful induration after travel. Over months, she experienced forearm induration and neuropathic hand pain; examination revealed bilateral lower leg peau d'orange and a right forearm groove sign. Laboratory evaluation showed episodic peripheral eosinophilia and an IgA-κ monoclonal gammopathy with nephrotic-range proteinuria. Electromyography confirmed bilateral median neuropathy at the wrists. Empiric prednisone produced marked symptomatic improvement. Bone marrow evaluation was consistent with monoclonal gammopathy of undetermined significance (MGUS). Kidney biopsy showed no amyloid, monoclonal immunoglobulin deposition disease (MIDD), proliferative glomerulonephritis with monoclonal deposits (PGNMID), light-chain cast nephropathy, or light-chain tubulopathy - making monoclonal gammopathy of renal significance (MGRS) unlikely. The hallmark cutaneous signs of EF (groove sign, peau d'orange) and limb-predominant involvement favored EF over mimics such as scleredema, morphea profunda, and systemic sclerosis. MRI is useful to confirm fascial involvement and guide biopsy when patients hesitate about incisional sampling. EF is classically steroid-responsive; methotrexate or mycophenolate are common steroid-sparing agents, with biologics or intravenous immunoglobulin (IVIG) reserved for refractory disease. The patient also had MGUS and carpal tunnel syndrome - both conditions that may raise concern for amyloidosis; however, amyloid was excluded histopathologically. This case highlights EF associated with IgA-κ MGUS and significant proteinuria, in which a kidney biopsy excluded MGRS lesions, illustrating the importance of multidisciplinary evaluation and targeted tissue diagnosis. Prompt recognition of EF's bedside signs can expedite treatment and functional recovery while more invasive diagnostics are considered.