Relapsing Polychondritis

• Type II Collagen and Cartilage Antigen Recognition: The primary pathogenic mechanism involves dysregulated T cell and B cell responses to type II collagen and other cartilage matrix components (including proteoglycans and matrilin-1). Autoreactive CD4+ T cells recognize processed epitopes from these antigens presented on MHC class II molecules, leading to activation of cartilage-specific helper T cells. B cells produce anti-cartilage antibodies, particularly targeting type II collagen and other cartilage-associated proteins. These antibodies form immune complexes that deposit in cartilage tissue and activate complement through the classical pathway. The initial trigger for loss of immune tolerance remains unclear but may involve molecular mimicry (cross-reactivity with pathogenic organisms), epitope spreading from a primary antigenic target, or genetic predisposition in conjunction with environmental triggers.

• Complement Activation and Neutrophilic Inflammation: Immune complex deposition in cartilage activates the complement cascade, particularly via C3a and C5a generation, which are potent neutrophil chemoattractants. Activated neutrophils infiltrate cartilage tissue and release substantial quantities of proteolytic enzymes (elastase, collagenase, matrix metalloproteinases—particularly MMP-1, MMP-8, and MMP-13) and reactive oxygen species. These mediators directly degrade the extracellular matrix components of cartilage, including type II collagen (the primary structural protein of hyaline cartilage), proteoglycans, and elastic fibers. The perpetuation of neutrophilic inflammation through continuous chemotaxis and enzyme release drives progressive cartilage destruction in affected sites. This explains the recurrent, episodic nature of inflammation: acute flares involve intense neutrophilic infiltration and enzyme release, while quiescent periods show relative immune quiescence but ongoing irreversible tissue damage.

• Structural Cartilage Changes and Tissue Remodeling: Chronic inflammation and enzymatic degradation result in progressive loss of cartilage matrix architecture and replacement with fibrosis and calcification. In the ears, cartilage becomes softened, irregular, and eventually may calcify or undergo fibrosis, leading to floppy, collapsed auricular structures. In the tracheobronchial tree, cartilage rings become irregularly ossified or destroyed, causing loss of structural support and malacia (softening) of airways, with subsequent dynamic airway collapse during expiration. Joint cartilage erosion leads to secondary osteoarthritis-like changes. Vascular involvement occurs through infiltration of vessel walls with inflammatory cells and can lead to vasculitis affecting medium-sized vessels, contributing to systemic manifestations. The chronic nature of cartilage degradation explains the progressive and irreversible nature of anatomic deformities in untreated disease.

• Idiopathic Primary Relapsing Polychondritis (75% of cases): The majority of RP cases occur without identifiable associated systemic disease. Genetic predisposition appears relevant, as HLA-DR4 and HLA-DQ8 associations have been described in some populations, though no strong genetic determinant has been definitively established. Presumed environmental triggers (viral infections, chemical exposures) may initiate autoimmunity in genetically susceptible individuals through molecular mimicry mechanisms or adjuvant effects. The lack of defined etiology makes primary RP an idiopathic autoimmune condition similar to many systemic autoimmune diseases.

• Secondary Relapsing Polychondritis Associated with Systemic Autoimmune Diseases (25% of cases): RP frequently occurs in conjunction with other connective tissue disorders, most commonly systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA). Other significant associations include Sjögren syndrome, scleroderma, vasculitis (particularly antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis), and inflammatory bowel disease (IBD), particularly ulcerative colitis. The presence of underlying systemic autoimmunity provides evidence that RP represents a manifestation of broader immune dysregulation and suggests shared pathogenic mechanisms involving loss of tolerance to multiple self-antigens. Secondary RP typically presents concurrently with or during the course of the associated systemic disease.

• Malignancy-Associated Relapsing Polychondritis: Approximately 5-10% of RP cases are associated with underlying malignancy, most frequently hematologic malignancies (lymphomas, leukemias) or solid tumors. The paraneoplastic association suggests that tumor-derived antigens may cross-react with cartilage antigens or that malignancy-related immune dysregulation unmasks autoreactive responses. Malignancy-associated RP may present de novo in older adults without prior autoimmune disease history and should prompt malignancy screening.

• Drug-Induced and Environmental Triggers: Case reports suggest possible associations with certain medications (particularly immunologic agents, antibiotics) and occupational exposures, though causality remains unproven. These are not established risk factors but warrant consideration in temporal relationships to disease onset.

• Auricular Inflammation (Most Common and Earliest Manifestation): Acute inflammation of the external ear occurs in 80-90% of patients, often as the initial presentation. Patients develop sudden onset of pain, erythema, edema, and warmth affecting the ear cartilage but classically sparing the non-cartilaginous earlobe—this sparing is a pathognomonic clinical finding highly suggestive of RP and distinguishing it from other causes of auricular inflammation. The inflammation may begin in one ear and progress bilaterally. Recurrent flares lead to progressive deformity of the auricle, with cartilage becoming floppy, wrinkled, and atrophic, creating a characteristic "cauliflower ear" appearance. Otoscopy may reveal inflammation of the cartilaginous external auditory canal. Conductive or sensorineural hearing loss can occur through middle ear involvement (including inflammation of the ossicles) or through eighth cranial nerve involvement.

• Nasal Involvement: The nasal cartilage becomes inflamed and progressively destroyed, leading to nasal bridge collapse and a characteristic "saddle nose" deformity visible on frontal view. Patients report nasal pain, epistaxis, rhinitis symptoms, and progressive loss of nasal dorsal height. The collapsed bridge creates a depression where a normal nasal dorsum should project, resembling the shape of a saddle. This is a classic, pathognomonic deformity in advanced RP and serves as a key diagnostic clue on examination.

• Tracheobronchial Involvement (Most Life-Threatening): Progressive inflammation and destruction of tracheal and bronchial cartilage rings occur in 25-50% of patients and represent the most dangerous manifestation. Patients develop recurrent respiratory symptoms including stridor (indicating upper airway involvement), dyspnea, chronic cough, and recurrent respiratory infections. As cartilage rings are destroyed, malacia develops with dynamic airway collapse, particularly during expiration when increased intraluminal pressure causes collapse of weakened airways. This can present acutely as dyspnea or stridor during acute flares or progressively as chronic airflow obstruction. Severe airway disease may require intubation or tracheostomy. High-resolution CT imaging shows irregular cartilage destruction, tracheal narrowing, and loss of normal cartilage ring appearance.

• Arthritis and Joint Involvement: A non-erosive, inflammatory polyarthritis occurs in 25-50% of patients, often migratory and episodic corresponding with systemic flares. Typically affects the knees, ankles, shoulders, wrists, and proximal interphalangeal joints. Distinguishing features include lack of erosions on radiographs (despite radiographic evidence in some cases) and potential for recurrent flares at the same or different sites. Joint involvement may resemble rheumatoid arthritis or lupus arthritis but lacks the typical serologic findings of these conditions in primary RP.

• Ocular Manifestations (20-30% of patients): Inflammation can affect multiple ocular structures. Episcleritis and scleritis cause localized or diffuse eye pain, photophobia, and injection. Keratitis and corneal ulceration can develop, potentially threatening vision. Anterior uveitis with iris involvement presents with photophobia and eye pain. Iritis with posterior synechiae formation may develop. Retinal vasculitis can occur, presenting with visual symptoms or floaters. The varied ocular manifestations reflect the broad distribution of cartilage throughout the eye.

• Laryngeal Involvement: The laryngeal cartilage structures (arytenoid, cricoid, thyroid cartilages) become inflamed, causing hoarseness, voice changes, sore throat, and potentially acute airway obstruction if edema is severe. Laryngoscopy reveals erythema and edema of laryngeal structures.

• Cardiac and Vascular Involvement (5-10%): Aortitis can develop through inflammation of the aortic wall, potentially leading to aortic regurgitation, aortic aneurysm formation, and aortic dissection—serious life-threatening complications. Myocarditis, pericarditis, and cardiac conduction abnormalities can occur. Systemic vasculitis affecting medium and small vessels may contribute to various organ manifestations.

• Systemic and Constitutional Symptoms: Patients may experience low-grade fever, malaise, fatigue, and weight loss during acute flares. These non-specific symptoms reflect systemic inflammation. Episodic pattern is characteristic: acute flares lasting days to weeks with complete or partial resolution between episodes, though recurrent flares lead to cumulative permanent damage.

• Cutaneous and Subcutaneous Manifestations: Non-specific rashes, urticaria, or nodules may develop in some patients. Erythema nodosum has been reported.

• Clinical Diagnostic Criteria (Mikuls and Vollertsen Modified from Damiani and Levine): The most widely used diagnostic approach requires the presence of three or more of the following major criteria, or chondritis of two or more anatomic sites plus at least one systemic manifestation, or chondritis of one or more anatomic sites plus positive genetic or histologic evidence:
• Bilateral auricular chondritis (recurrent, documented inflammation with sparing of the earlobe—the pathognomonic earlobe sparing is the key diagnostic feature)
• Non-erosive inflammatory polyarthritis
• Nasal chondritis (leading to saddle nose deformity)
• Ocular inflammation (episcleritis, scleritis, keratitis, uveitis)
• Respiratory tract chondritis (stridor, subglottic stenosis, tracheobronchial involvement)
• Audiovestibular damage (sensorineural hearing loss, tinnitus, vertigo)

• Histopathology: Auricular or nasal cartilage biopsy represents the most definitive diagnostic test, demonstrating characteristic findings: loss of the normal basophilic staining of cartilage matrix due to loss of glycosaminoglycans, inflammatory infiltrate of lymphocytes, plasma cells, and neutrophils, degradation of cartilage lacunae, and absence of calcification (distinguishing from other cartilage diseases). Biopsy of affected cartilage confirms diagnosis when clinical presentation is unclear. The absence of specific inflammation in biopsy specimens effectively excludes RP in the differential.

• Laboratory Findings: No specific laboratory test is pathognomonic for RP. Inflammatory markers (erythrocyte sedimentation rate [ESR] and C-reactive protein [CRP]) are typically elevated during active flares and help assess disease activity but may normalize between flares. Antinuclear antibody (ANA) is positive in approximately 50% of primary RP cases (often in low to moderate titers) and more frequently in secondary RP associated with SLE. Rheumatoid factor (RF) and anti-CCP antibodies are negative in primary RP unless associated with RA. Antibodies against type II collagen have been demonstrated in RP patients but are not routinely measured and lack clinical utility for diagnosis. Complete blood count may show mild anemia of chronic inflammation. Thyroid function should be assessed given the association with autoimmune thyroiditis.

• Imaging Studies:
• Auricular imaging: High-resolution CT or MRI of the temporal bone can reveal auricular cartilage destruction, calcification, and erosive changes but is not required for diagnosis when clinical features are clear.
• Tracheobronchial imaging: High-resolution CT of the chest demonstrates tracheal and bronchial wall abnormalities including cartilage irregularity, tracheal narrowing (reduced diameter), loss of normal cartilage ring appearance, areas of malacia, and potential subglottic stenosis. Expiratory CT imaging can dynamically demonstrate airway collapse. This imaging is critical for assessing respiratory involvement severity and determining need for intervention.
• Nasal imaging: CT or MRI of the sinuses demonstrates nasal bridge erosion and cartilage destruction.
• Cardiac imaging: Chest X-ray or CT may show aortic dilation or aortic calcification in patients with aortitis. Echocardiography is essential for evaluating cardiac involvement, assessing for aortic regurgitation, and measuring aortic root dimensions to detect aneurysm formation.

• Pulmonary Function Testing: For patients with respiratory symptoms, spirometry demonstrates a characteristic pattern of fixed airflow obstruction (reduced FEV₁ with reduced FEV₁/FVC ratio that does not improve significantly with bronchodilators), reflecting the fixed nature of tracheobronchial malacia. Flow-volume loops may show flattening of the expiratory limb consistent with fixed obstruction. These findings can precede radiographic changes and help detect early respiratory involvement.

• Otologic Assessment: Audiometry and videonystagmography help document sensorineural hearing loss and vestibular dysfunction. Tuning fork examination may reveal sensorineural hearing loss.

• Differential Diagnosis Considerations:
• Relapsing fever (Borrelia recurrentis or Borrelia hermsii): Presents with recurrent fever and systemic symptoms but lacks cartilage involvement; spirochetes visible on blood smears.
• Recurrent cellulitis or auricular infection: Typically affects the earlobe (which is spared in RP), responds to antibiotics, and lacks the systemic manifestations and multi-site involvement of RP.
• Granulomatosis with polyangiitis (GPA, formerly Wegener's granulomatosis): Can cause nasal deformity and respiratory involvement but is distinguished by necrotizing vasculitis, glomerulonephritis, positive c-ANCA/PR3 antibodies, and necrotizing granulomatous inflammation on biopsy.
• Systemic lupus erythematosus: May present with arthritis and constitutional symptoms but distinguished by typical lupus serologies (high-titer ANA, anti-dsDNA, anti-Smith antibodies), presence of lupus nephritis or hemolytic anemia, and absence of pathognomonic cartilage involvement patterns.
• Rheumatoid arthritis: Causes arthritis and can involve ears, but defined by RF/anti-CCP positivity, erosive joint disease, and different pattern of auricular involvement.

• First-Line Therapy: Corticosteroids: Systemic corticosteroids

Airway complications (leading cause of disease-related death)

• Tracheobronchomalacia and dynamic expiratory collapse — emergency: without rigid cartilage rings, the airway wall cannot resist the positive pleural/extraluminal pressure generated during forced expiration; once extraluminal pressure exceeds intraluminal airway pressure, the malacic segment collapses. Signaled by stridor, positional dyspnea, or a flattened expiratory limb on flow-volume loop. Acute obstruction may require intubation, silicone/metallic stenting, or CPAP as a pneumatic stent; a standard tracheostomy does not relieve distal bronchomalacia.
• Subglottic stenosis: fixed fibrotic narrowing after repeated cricoid/laryngeal chondritis; suspect with biphasic stridor and hoarseness that fails to improve with steroids.
• Recurrent pneumonia and bronchiectasis: impaired mucociliary clearance behind malacic segments.

Cardiovascular complications

• Aortic root dilation with aortic regurgitation: aortitis destroys the elastic media, producing a widened pulse pressure and diastolic murmur; serial echocardiography is warranted.
• Aortic aneurysm and dissection — emergency: tearing chest/back pain with pulse or blood-pressure differential demands immediate CT angiography.
• Conduction block, myocarditis, pericarditis: inflammatory involvement of the conduction system may present as syncope or new heart block.

Sensory and structural complications

• Necrotizing scleritis / peripheral ulcerative keratitis — urgent: boring eye pain with vision loss risks globe perforation; same-day ophthalmology referral.
• Sensorineural hearing loss and vertigo: vasculitis of the internal auditory artery, not cartilage destruction.
• Irreversible cauliflower ear and saddle-nose deformity: cumulative damage from flares, not active inflammation — steroids will not reverse them.

Treatment-related complications

• Glucocorticoid toxicity: osteoporosis, hyperglycemia, cataract, adrenal suppression, avascular necrosis; the ACR guideline on glucocorticoid-induced osteoporosis supports calcium/vitamin D plus bisphosphonate or other antiresorptive therapy in patients at elevated fracture risk on chronic steroids.
• Immunosuppression-related infection: opportunistic infection (including Pneumocystis jirovecii) with steroid-sparing agents; screen for latent tuberculosis and hepatitis B before TNF inhibitors, and avoid live vaccines per CDC/ACIP guidance for immunocompromised hosts.
• Cyclophosphamide: hemorrhagic cystitis, bladder malignancy, gonadal failure — persistent hematuria is the alerting sign.
• Methotrexate: transaminitis, cytopenias, hypersensitivity pneumonitis.

• Earlobe sparing is the single tested finding: an erythematous, exquisitely tender auricle with a soft, uninvolved lobule localizes inflammation to cartilage. A red, swollen ear that includes the lobule is cellulitis/erysipelas. Infectious perichondritis also spares the lobule but is typically unilateral and follows trauma, piercing, or surgery — antibiotics, not steroids.
• Saddle nose + respiratory symptoms is the classic fork in the road: check ANCA/PR3 and urinalysis. Positive c-ANCA with glomerulonephritis and necrotizing granulomas means granulomatosis with polyangiitis; RP has neither. Cocaine-induced midline destruction (septal perforation, positive urine toxicology, atypical p-ANCA/anti-HNE) is the other distractor.
• Stridor or exertional dyspnea is the emergency stem: the best next step is airway assessment — flow-volume loop showing fixed or variable intrathoracic obstruction plus dynamic inspiratory/expiratory CT of the chest. Do not settle for a bronchodilator trial; malacia is not reversible obstruction and will not respond.
• Diagnosis is clinical, not histologic: recurrent chondritis at characteristic sites suffices. Biopsy is reserved for atypical cases; a question that offers "cartilage biopsy" for a patient with bilateral auricular chondritis, saddle nose, and scleritis is offering the distractor.
• The association examiners love: VEXAS syndrome — somatic UBA1 mutation in older men presenting with chondritis, fevers, cutaneous neutrophilic dermatosis, vacuoles in myeloid precursors, and myelodysplastic syndrome. More broadly, roughly a quarter of RP cases accompany another autoimmune disease, and hematologic malignancy screening is appropriate in older patients.
• Arthritis is non-erosive, seronegative, migratory, and often involves the costochondral and sternoclavicular joints — anterior chest wall pain in a patient with a floppy ear is RP, not costochondritis.
• Treatment logic: mild auricular/nasal disease responds to NSAIDs or low-dose glucocorticoids; any airway, ocular, or cardiovascular involvement is organ-threatening and demands high-dose systemic glucocorticoids with a steroid-sparing immunosuppressant.
• MAGIC syndrome (mouth and genital ulcers with inflamed cartilage) is the Behçet–RP overlap buzzword.