Natural History of Granulomatosis With Polyangiitis: Clinical and Genetic Biomarkers of Airway Disease NoAAC PR-03 Study

Granulomatosis with polyangiitis (GPA, formerly known as Wegener's granulomatosis) is a rare multisystem necrotizing granulomatous vasculitis of small and medium vessels. Nearly 20% of GPA patients suffer life-threatening obstruction of their airways. Even when survived, airway involvement can render patients in this disease subset unable to communicate, struggling to breath, and dependent on a tracheostomy for survival. Airway disease frequently leads to irreversible physiologic impairment and is highly correlated with reduced quality of life in GPA.

Prior to the 1970s, patients with GPA had a 1-year mortality rate of >80%, primarily due to renal or lung failure. The introduction of combination cyclophosphamide and glucocorticoid treatment 4 decades ago greatly improved patient outcomes, turning this into a more chronic long-term disease. However, while progress has been made in the development of successful treatment regimes for systemic disease, the role of current therapies in ameliorating the airway complications of GPA is unknown. The evolution of GPA into a chronic disease has brought the management of the airway manifestations of GPA to the forefront. The natural history of the airway disease in GPA has never been longitudinally characterized, and there are no reliable biomarkers of clinical outcome.

In GPA the incidence of airway stenosis localized to the anatomic region below the vocal cord (subglottic stenosis) has been estimated to be 16%-50%. It may occur in isolation as the presenting symptom of GPA, or as a late-stage manifestation of disease. Although stenosis is frequently limited to the subglottis, it may extend up to involve to vocal cords, or down to involve the distal trachea and bronchi. Unfortunately, studies have documented a relatively high incidence of multilevel airway involvement (34%) in GPA. In one series of 44 patients, one in five had evidence of laryngeal stenosis. Studies have also found a high incidence of metachronous bronchial disease.

Laryngeal and Bronchial stenosis appear to be progressive and occur after the onset of subglottic stenosis, but the true natural history of airway involvement in GPA is unknown.

GPA is a member of the anti-neutrophil cytoplasmic antibody (ANCA) vasculitides. Given the strong association of GPA with ANCA production, much focus has been placed on understanding the mechanisms of ANCA production and pathogenesis. The factors by which ANCAs are initially generated are poorly understood. The majority of in vitro and animal model research implicating neutrophils and T cells as the principal inflammatory cells in GPA is surprising given the known impressive clinical treatment response to B cell depletion with rituximab. This discordance reinforces that the knowledge gap between pathogenesis and therapy is GPA is wide.

The distinction between focused airway disease and severe systemic disease has important therapeutic implications. The course of airway stenosis in GPA has been found to run independently of the systemic disease course and is often refractory to standard systemic therapy. In one representative case series, subglottic stenosis (SGS) was diagnosed in 49% of patients while they were receiving systemic treatment, and 56% of the patients who required tracheostomies did so despite having been treated for at least 2 months with systemic immunosuppressive agents. Developing novel therapeutics to control airway-focused GPA and prevent the development and/or progression of destructive airway damage is desperately needed.

Because of the small numbers of patients affected, and with clinical experience dispersed among a small number of clinical referral centers, the natural history of rare diseases is often poorly described. When knowledge about disease is insufficient to guide clinical development, well-designed natural history studies are critical to developing and proving the efficacy of novel therapeutics.