A neuropathic masquerade: deciphering chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) secondary to granulomatosis with polyangiitis (GPA)

Abstract

Case Presentation: A 64-year-old male with hypertension presented with a 12-week history of 13 kg weight loss, ascending paresthesia, severe allodynia, and progressive tetraparesis resulting in walker dependence. Auditory acuity loss and sporadic fever were also noted. Physical examination revealed symmetrical tetraparesis, global areflexia, muscle atrophy, "glove-and-stocking" hypoesthesia with impaired proprioception and sensory ataxia. Electroneuromyography (ENMG) fulfilled EAN/PNS 2021 criteria for a primarily demyelinating polyradiculoneuropathy (CIDP), showing prolonged distal latencies, reduced conduction velocities, and proximal F-wave blocks. CSF analysis showed albuminocytologic dissociation (81 mg/dL protein; 0 cells). Systemic investigation revealed hematuria, proteinuria (1.6g/24h), renal dysfunction, and reactive PR3-ANCA (32.6 U/mL). Chest CT identified pulmonary nodules with the "feeding vessel sign." A renal biopsy demonstrated focal necrotizing crescentic glomerulonephritis with granulomatous arteritis, confirming Granulomatosis with Polyangiitis (GPA). The patient received methylprednisolone pulse therapy (1g/day) for five days, achieving significant clinical remission. A long-term immunosuppression plan was established in coordination with the Nephrology team. Discussion: CIDP is an immune-mediated disorder of the peripheral nervous system that, while often idiopathic, may manifest as a secondary phenotype of systemic diseases. Although GPA-associated neuropathy typically presents as mononeuritis multiplex due to ischemic axonal injury from vasa nervorum vasculitis, this case illustrates a rare presentation of symmetric, inflammatory demyelinating polyradiculoneuropathy mimicking typical CIDP. This clinical presentation is rare, and the current medical literature contains only isolated case reports, with no data from epidemiological or population-based studies to estimate the prevalence or incidence of the neurological findings within the context of patients with GPA. The multisystemic involvement involving the auditory, pulmonary, and renal systems is a hallmark of GPA. The diagnostic challenge lies in the prominent CSF protein elevation and the ENMG findings, which could lead to a misdiagnosis of idiopathic CIDP if not for the systemic markers. The presence of PR3-ANCA and the biopsy-proven crescentic glomerulonephritis were pivotal in identifying the vasculitic process as the primary driver of the demyelinating response. Final Comments: This case illustrates that a CIDP phenotype can be the sentinel manifestation of systemic disease. Relying solely on electrophysiological criteria without investigating multisystemic "red flags" can lead to diagnostic oversight. Here, the neurological syndrome was secondary to Granulomatosis with Polyangiitis. Differentiating idiopathic from secondary CIDP is fundamental to initiate etiology-specific induction therapy, which is essential for systemic control and the prevention of irreversible axonal loss or permanent disability.