11.3 Cutaneous Vasculitis & Neutrophilic Dermatoses

11.3 Cutaneous Vasculitis & Neutrophilic Dermatoses

Cutaneous Vasculitis: Classification & Vessel Size Paradigm

Cutaneous vasculitis comprises a heterogeneous group of inflammatory diseases characterized by destruction of blood vessel walls. In dermatological practice, diagnostic classification is anchored to the 2012 Revised Chapel Hill Consensus Conference (CHCC) Nomenclature, adapted to vessel caliber in cutaneous tissue:

1. Small-Vessel Vasculitis (SVV): Affects postcapillary venules, arterioles, and capillaries in the superficial/mid-dermis. Hallmark morphology: Palpable purpura.
2. Medium-Vessel Vasculitis (MVV): Affects muscular arteries at the dermal-subcutaneous fat junction and panniculus. Hallmark morphology: Subcutaneous nodules, livedo racemosa, punched-out necrotic ulcers, digital gangrene.
3. Large-Vessel Vasculitis (LVV): Giant cell arteritis and Takayasu arteritis; primarily extracutaneous, but can manifest scalp necrosis or limb claudication.

                                    ┌────────────────────────────────────────────────────────┐
                                    │             Cutaneous Vasculitis Spectrum              │
                                    └───────────────────────────┬────────────────────────────┘
                                                                │
                ┌───────────────────────────────────────────────┴───────────────────────────────────────────────┐
                │                                                                                               │
┌───────────────▼───────────────┐                                                               ┌───────────────▼───────────────┐
│    Small-Vessel Vasculitis    │                                                               │    Medium-Vessel Vasculitis   │
│    (Postcapillary Venules)    │                                                               │  (Muscular Arteries / Fat Jct)│
└───────────────┬───────────────┘                                                               └───────────────┬───────────────┘
                │                                                                                               │
                ├─ Cutaneous Leukocytoclastic Vasculitis (CLCV)                                                 ├─ Systemic Polyarteritis Nodosa (PAN)
                ├─ IgA Vasculitis (Henoch-Schönlein purpura)                                                    │  (HBV-associated, microaneurysms, spares lungs)
                ├─ Urticarial Vasculitis (NUV vs HUV)                                                           └─ Cutaneous PAN (cPAN)
                ├─ Cryoglobulinaemic Vasculitis (Type I / II / III)                                                (Livedo racemosa, tender nodules, benign course)
                └─ ANCA-Associated Vasculitides (AAV):
                   ├─ Granulomatosis with Polyangiitis (GPA; c-ANCA / PR3)
                   ├─ Microscopic Polyangiitis (MPA; p-ANCA / MPO)
                   └─ Eosinophilic GPA (EGPA; p-ANCA / MPO, asthma, eosinophils)

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Small-Vessel Vasculitides

1. Cutaneous Leukocytoclastic Vasculitis (CLCV)

CLCV (hypersensitivity vasculitis) is the most common cutaneous vasculitis. It is confined to the skin in up to 70% of cases or represents the cutaneous manifestation of systemic immune-complex disease.

• Clinical Presentation: Palpable purpura—non-blanching, 1 to 3 mm discrete or coalescing violaceous papules. Lesions demonstrate a strict gravity-dependent distribution, concentrating on the lower legs, ankles, and feet (or over sacral pressure points in bedridden patients). Lesions may develop central hemorrhagic vesicles, bullae, or superficial ulcerations.
• Etiological Triggers:
  • Infections (~30%): Group A beta-hemolytic streptococcal upper respiratory infections, hepatitis B/C, HIV, infective endocarditis.
  • Medications (~15–20%): Beta-lactams, sulfonamides, NSAIDs, thiazides, allopurinol, propylthiouracil, hydralazine.
  • Systemic Autoimmune Diseases (~15%): SLE, rheumatoid arthritis, Sjögren syndrome.
  • Malignancies (~5%): Paraneoplastic, predominantly lymphoproliferative disorders (multiple myeloma, hairy cell leukemia, lymphoma) and solid tumors.
  • Idiopathic (~40–50%): Exhaustive clinical workup reveals no identifiable trigger.

Histopathology & The Critical Direct Immunofluorescence (DIF) Window

• H&E Histological Triad of CLCV:
  1. Fibrinoid Necrosis: Deposition of homogeneous, eosinophilic, smudgy fibrin within the walls of postcapillary venules.
  2. Neutrophilic Infiltrate with Leukocytoclasia: Dense transmural and perivascular neutrophils undergoing apoptotic degeneration and nuclear fragmentation (karyorrhexis), producing scattered basophilic fragments known as "nuclear dust".
  3. Erythrocyte Extravasation & Endothelial Swelling: Red blood cells leaking through breached venular walls into the surrounding dermis (generating the non-blanching purpuric color), accompanied by plump, damaged endothelial cells.
• THE 24-TO-48-HOUR DIF WINDOW RULE (KEY FACT):
  • Punch biopsy for direct immunofluorescence (DIF) must be taken from a fresh, early lesion (<24 to 48 hours old).
  • In lesions older than 48 hours, migrating neutrophils and tissue macrophages phagocytose and degrade the vascular immune complexes and complement fragments, yielding a false-negative DIF result.
  • DIF reveals granular perivascular deposits of C3, IgM, IgG, or IgA within venular walls.

2. IgA Vasculitis (IgAV / Henoch-Schönlein Purpura)

IgA vasculitis is an immune-complex small-vessel vasculitis mediated by the deposition of abnormal galactose-deficient IgA1 (Gd-IgA1) immune complexes.

• Epidemiology: The most common systemic vasculitis in pediatric patients (peak incidence 4–7 years), but occurs in adults, where it carries a significantly higher risk of chronic, progressive renal disease.
• The Classical Diagnostic Tetrad:
  1. Palpable Purpura: Symmetrically distributed across the extensor lower extremities, buttocks, and perineum; generally spares the trunk and face in children.
  2. Arthralgia / Arthritis: Non-erosive, periarticular swelling affecting knees and ankles (up to 75%).
  3. Gastrointestinal Symptoms (50–75%): Colicky abdominal pain, nausea, vomiting, bowel ischaemia, and gastrointestinal haemorrhage (melaena/haematochezia). Intussusception is uncommon (a few per cent of children) and, unlike idiopathic childhood intussusception, is usually ileo-ileal.
  4. Renal Involvement (IgA Nephropathy): Mesangial proliferative glomerulonephritis; manifests as microscopic hematuria, red cell casts, proteinuria, hypertension, or nephrotic syndrome (40–50%).
• Direct Immunofluorescence Hallmark: Bright, granular, vascular IgA deposition (frequently with C3) in the walls of superficial dermal postcapillary venules.
• Mandatory Surveillance Protocol: Renal involvement dictates long-term prognosis. European guidelines mandate regular screening with blood pressure and urinalysis (proteinuria/hematuria) at diagnosis, weekly for the first month, biweekly through month 3, and monthly for at least 6 months.

3. Urticarial Vasculitis

Characterized by urticarial wheals that demonstrate vasculitic features upon clinical and histological scrutiny.

• Clinical Discriminators (Urticaria vs Urticarial Vasculitis):
  • Individual lesion duration: Ordinary urticaria resolves within <24 hours in a given site; urticarial vasculitis plaques persist >24 to 72 hours in the exact same location.
  • Sensory symptoms: Ordinary urticaria is intensely pruritic; urticarial vasculitis wheals cause burning, stinging, or tenderness.
  • Resolution morphology: Resolves with residual purpura or post-inflammatory hyperpigmentation (hemosiderin staining) due to red blood cell extravasation.
  • Histopathology: Demonstrates true leukocytoclastic vasculitis.
• Classification & Systemic Association:
  • Normocomplementaemic Urticarial Vasculitis (NUV): Normal serum C3/C4/C1q; usually idiopathic, benign, cutaneous-limited, with low systemic risk.
  • Hypocomplementaemic Urticarial Vasculitis (HUV): Markedly depressed C3, C4, and C1q, with circulating anti-C1q autoantibodies.
  • HUV is strongly associated with underlying SLE or represents Hypocomplementaemic Urticarial Vasculitis Syndrome (HUVS / McDuffie Syndrome): characterized by severe obstructive pulmonary disease (severe emphysema, chronic cough), recurrent angioedema, ocular inflammation (episcleritis, uveitis), and glomerulonephritis.

4. Cryoglobulinaemic Vasculitis

Cryoglobulins are immunoglobulins that reversibly precipitate in vitro at temperatures <37°C and redissolve upon rewarming.

• Brouet Classification:
  • Type I (Monoclonal): Monoclonal IgG or IgM (without rheumatoid factor activity). Associated with hematologic malignancies: multiple myeloma, Waldenström macroglobulinemia, monoclonal gammopathy of undetermined significance (MGUS). Pathogenesis: Non-inflammatory vascular occlusion and hyperviscosity. Morphology: Acrocyanosis, digital gangrene, cold-induced retiform purpura, livedo, punched-out leg ulcers.
  • Type II (Mixed Cryoglobulinemia): Monoclonal IgM (with rheumatoid factor activity) directed against polyclonal IgG. Strongly associated with Hepatitis C Virus (HCV) infection (>80–90%).
  • Type III (Mixed Cryoglobulinemia): Polyclonal IgM (with RF activity) directed against polyclonal IgG. Associated with HCV, chronic infections, SLE, and Sjögren syndrome.
• Clinical Presentation in Mixed Cryoglobulinemia (Type II & III):
  • Meltzer's Triad: Palpable purpura (lower legs), arthralgias, and asthenia (severe fatigue).
  • Peripheral sensorimotor polyneuropathy (mononeuritis multiplex) and membranoproliferative glomerulonephritis (MPGN).
• Diagnostic Serology: Profoundly depressed serum C4 is universal (often undetectable, while C3 is mildly reduced or normal); positive rheumatoid factor (RF); detectable cryocrit (blood collection and transport must strictly occur in pre-warmed tubes maintained at 37°C prior to clotting to avoid false-negative results!). First-line therapy for HCV-associated mixed cryoglobulinemia: direct-acting antiviral (DAA) therapy ± rituximab.

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ANCA-Associated Vasculitides (AAV)

AAV encompasses systemic necrotizing small-vessel vasculitides linked to antineutrophil cytoplasmic antibodies (ANCA):

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Medium-Vessel Vasculitis: Polyarteritis Nodosa (PAN)

Polyarteritis nodosa is a systemic or cutaneous necrotizing arteritis targeting medium-sized and small muscular arteries. Crucial Rule: PAN spares postcapillary venules and arterioles, does not cause glomerulonephritis, and does not involve pulmonary circulation.

1. Systemic Polyarteritis Nodosa (sPAN)

• Etiology: Strongly associated with Hepatitis B Virus (HBV) surface antigenemia (immune complex deposition), as well as idiopathic and genetic forms (deficiency of adenosine deaminase 2 [DADA2]).
• Clinical Manifestations: Systemic hypertension (renal artery vasculitis inducing ischemia), renal microaneurysms (demonstrated on mesenteric/renal digital subtraction angiography), peripheral neuropathy (asymmetric wrist/foot drop: mononeuritis multiplex), gastrointestinal ischemia/infarction, orchitis/testicular pain.

2. Cutaneous Polyarteritis Nodosa (cPAN)

• Clinical Scope: A chronic, relapsing, benign form confined entirely to the skin and peripheral neuromuscular system of the limbs, without visceral involvement.
• Cutaneous Morphology:
  • Tender Subcutaneous Nodules: Painful, 0.5 to 2 cm subcutaneous nodules distributed along the course of muscular arteries on the lower legs.
  • Livedo Racemosa: Irregular, broken, asymmetric, jagged violaceous reticular rings that do not reverse with warmth (unlike physiologic livedo reticularis).
  • "Starburst" Livedo: Clusters of branching livedoid macules surrounding malleolar ulcerations.
  • Punched-Out Ulcerations & Digital Gangrene: Secondary to ischemic occlusion.
• THE BIOPSY TECHNIQUE PEARL (KEY PITFALL):
  • Standard punch biopsies are inadequate and yield false-negative results because they only sample the superficial dermis.
  • Definitive diagnosis requires a deep incisional or wedge biopsy down into the subcutaneous fat, specifically targeting the active, indurated margin of a tender nodule to capture muscular arteries at the dermal-subcutaneous junction.
  • Histology shows transmural segmental necrotizing arteritis of muscular arteries with fibrinoid necrosis, internal elastic lamina disruption (Verhoeff-van Gieson stain), and mixed neutrophil/mononuclear infiltration.

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Neutrophilic Dermatoses Spectrum

Neutrophilic dermatoses are non-infectious, autoinflammatory conditions characterized by dense, sheet-like dermal neutrophilic infiltration in the complete absence of primary leukocytoclastic vasculitis or microbial pathogens.

                                    ┌────────────────────────────────────────────────────────┐
                                    │             Neutrophilic Dermatoses Spectrum           │
                                    └───────────────────────────┬────────────────────────────┘
                                                                │
                                ┌───────────────────────────────┴───────────────────────────────┐
                                │                                                               │
                ┌───────────────▼───────────────┐                               ┌───────────────▼───────────────┐
                │     Pyoderma Gangrenosum      │                               │        Sweet Syndrome         │
                │             (PG)              │                               │  (Acute Febrile Neutrophilic) │
                └───────────────┬───────────────┘                               └───────────────┬───────────────┘
                                │                                                               │
                                ├─ Sterile follicular pustule / nodule                          ├─ Sudden tender erythematous succulent plaques
                                ├─ Painful ulcer with undermined violaceous border              ├─ "Pseudovesicular" mamillated surface
                                ├─ Cribriform "cigarette-paper" scarring                        ├─ High spiking fevers (>38°C)
                                ├─ Pathergy phenomenon (NO surgical debridement!)               ├─ Peripheral neutrophilic leukocytosis
                                ├─ Associations: IBD, MDS, IgA Gammopathy, RA                   ├─ Associations: AML/MDS, G-CSF, IBD, Infections
                                └─ First-line: Corticosteroids / Ciclosporin / Infliximab       └─ First-line: Systemic Corticosteroids (rapid)

1. Pyoderma Gangrenosum (PG)

Pyoderma gangrenosum is a sterile, ulcerative autoinflammatory neutrophilic dermatosis driven by hyperactive innate immunity, dysregulated neutrophil trafficking, and excessive pro-inflammatory cytokines (IL-1beta, IL-8, IL-17, TNF-alpha).

Clinical Morphology & Stages

• Primary Lesion: Begins acutely as an erythematous follicular papule, pustule, or fluctuant furunculoid nodule.
• Ulcerative Breakdown: Rapidly breaks down within days to form an excruciatingly painful ulcer.
• Hallmark Ulcer Edge: Violaceous, gunmetal-colored, ragged, edematous, overhanging, and deeply undermined border surrounded by a vibrant halo of erythema.
• Ulcer Base: Purulent, beefy-red granulation tissue covered with yellowish necrotic sludge, mucinous exudate, or hemorrhagic crust.
• Healing Architecture: Heals with characteristic cribriform (sieve-like, perforated) or "cigarette-paper" atrophic scars.
• Atypical Clinical Variants:
  • Bullous PG: Vesiculobullous lesions with central necrosis, predilection for upper extremities and face; strongly linked to hematologic malignancies (MDS, AML).
  • Pustular PG: Multiple sterile pustules surrounded by erythema; associated with active Inflammatory Bowel Disease flares.
  • Vegetative / Superficial Granulomatous PG: Indolent, superficial, non-undermined verrucous plaques; less aggressive, responds well to conservative or topical therapy.
  • Peristomal PG: Develops adjacent to abdominal stomas in patients with ulcerative colitis or Crohn's disease.

The Pathergy Phenomenon & Surgical Contraindication

• Pathergy: Induction of new inflammatory lesions or dramatic, catastrophic enlargement of existing ulcers following minor, trivial cutaneous trauma (venipuncture, needle sticks, surgical incisions, debridement).
• THE CARDINAL CLINICAL RULE / HIGH-STAKES EXAM POINT:
  • Sharp surgical debridement is strictly contraindicated in active pyoderma gangrenosum!
  • Aggressive surgical debridement or wedge excision performed under the mistaken diagnosis of a bacterial abscess, necrotizing fasciitis, or venous stasis ulcer induces rapid, explosive ulcer extension (pathergic exacerbation).
  • Incision and drainage of suspected abscesses must be deferred until PG is ruled out.

Systemic Disease Associations of PG

Up to 70% of pyoderma gangrenosum cases occur in association with an underlying systemic disorder:

1. Inflammatory Bowel Disease (~30%): Ulcerative Colitis (more frequent) > Crohn's disease. Note: PG activity does not always parallel the clinical activity of the underlying intestinal disease; ulcers can erupt during complete clinical remission of colitis.
2. Hematologic Malignancies & Gammopathies (~20%): Myelodysplastic Syndrome (MDS), Acute Myeloid Leukemia (AML), and Monoclonal Gammopathy (classically IgA Monoclonal Gammopathy).
3. Arthropathies (~15–20%): Rheumatoid arthritis, seronegative spondyloarthropathies.
4. Monogenic Autoinflammatory Syndromes: PAPA Syndrome (Pyogenic sterile Arthritis, Pyoderma gangrenosum, and severe cystic Acne; autosomal dominant mutation in PSTPIP1).

Validated Diagnostic Criteria (Delphi Consensus Criteria for Ulcerative PG)

Diagnosis requires meeting the Major Criterion plus at least 4 of 8 Minor Criteria:

• Major Criterion: Biopsy of ulcer edge showing a dense dermal neutrophilic infiltrate without evidence of infectious pathogens or true leukocytoclastic vasculitis.
• Minor Criteria:
  1. Exclusion of infection (negative bacterial, fungal, and mycobacterial cultures).
  2. Pathergy phenomenon (ulcer worsening after minor trauma or history of pathergy).
  3. History of Inflammatory Bowel Disease or inflammatory arthritis.
  4. History of papule, pustule, or vesicle ulcerating within 4 days of onset.
  5. Peripheral erythema, undermined border, and exquisite tenderness.
  6. Multiple ulcerations, at least one on an anterior lower leg.
  7. Cribriform or "cigarette paper" scarring at healed sites.
  8. Decrease in ulcer size within 1 month of initiating systemic immunosuppression.

European Management Guidelines for PG

• First-Line Systemic Therapy:
  • Systemic Corticosteroids: Oral prednisone (0.5 to 1.0 mg/kg/day) or intravenous pulsed methylprednisolone (1 g/day for 3 days) for rapid induction of remission.
  • Oral Ciclosporin: 3 to 5 mg/kg/day; in the randomised STOP-GAP trial, ciclosporin and prednisolone gave similar healing rates and similar overall adverse-event rates.
• Second-Line Biologic Therapy:
  • Infliximab: Chimeric anti-TNF-alpha monoclonal antibody (5 mg/kg at weeks 0, 2, 6, then every 8 weeks); the only biologic agent validated in a randomized, placebo-controlled trial for PG.
  • Adalimumab, Ustekinumab (anti-IL-12/23), Anakinra (IL-1 receptor antagonist).
• Wound Care: Gentle, non-adherent, absorbent dressings; negative pressure wound therapy (only after systemic disease is well controlled); avoid aggressive mechanical washing.

2. Sweet Syndrome (Acute Febrile Neutrophilic Dermatosis)

Sweet syndrome is characterized by the sudden onset of fever, peripheral neutrophilia, and tender cutaneous plaques driven by cytokine-mediated (G-CSF, IL-1, IL-6) neutrophil activation.

Clinical Triad & Morphology

1. Succulent Cutaneous Plaques: Abrupt onset of discrete, tender, edematous, erythematous-to-violaceous succulent papules, plaques, and nodules. The surface frequently exhibits a characteristic mamillated or "pseudovesicular" appearance (extreme, massive edema of the papillary dermis causing light reflection resembling fluid-filled vesicles, though needle aspiration yields no fluid).
2. Systemic Symptoms: High, spiking fevers (>38°C), malaise, headache, arthralgias, and myalgias.
3. Laboratory Markers: Marked peripheral blood neutrophilia (absolute neutrophil count >8,000/microL; >70% neutrophils), elevated C-reactive protein (CRP), and high ESR.

Diagnostic Criteria (Su & Liu / Modified von den Driesch Criteria)

Diagnosis requires meeting both Major Criteria and at least 2 of 4 Minor Criteria:

• Major Criteria:
  1. Abrupt onset of painful erythematous plaques or nodules.
  2. Histopathologic evidence of a dense, sheet-like dermal neutrophilic infiltrate without leukocytoclastic vasculitis.
• Minor Criteria:
  1. Pyrexia (fever > 38°C).
  2. Associated underlying condition: hematologic or visceral malignancy, inflammatory bowel disease, pregnancy, or preceding upper respiratory/gastrointestinal infection.
  3. Excellent and rapid response to systemic corticosteroid therapy.
  4. Abnormal laboratory values at presentation (3 of 4: ESR > 20 mm/hr, positive CRP, leukocytosis >8,000/microL, neutrophils >70%).

Malignancy-Associated Sweet Syndrome (MASS)

Approximately 15% to 20% of Sweet syndrome cases are paraneoplastic (MASS):

• Hematologic Neoplasms Predominate: Acute Myeloid Leukemia (AML) accounts for the vast majority, alongside myelodysplastic syndrome (MDS) and chronic myeloid leukemia.
• Atypical Diagnostic Clues for MASS:
  • Eruption of bullous, pustular, or ulcerative lesions that mimic pyoderma gangrenosum.
  • Prominent oral mucosal involvement (bullae, ulcers).
  • Absence of peripheral leukocytosis: Paradoxically, patients with MASS may present with cytopenias (anemia, neutropenia, or thrombocytopenia) due to underlying leukemic marrow infiltration!
  • Histopathology showing "histiocytoid" immature myeloid cells (Histiocytoid Sweet Syndrome).

Drug-Induced Sweet Syndrome

• Granulocyte Colony-Stimulating Factor (G-CSF / filgrastim, pegfilgrastim): The most common causative agent, occurring during neutrophil count recovery following chemotherapy.
• Other recognized drugs: All-trans retinoic acid (ATRA), bortezomib, trimethoprim-sulfamethoxazole, furosemide.

Management Protocol for Sweet Syndrome

• First-Line Therapy: Systemic Corticosteroids (Prednisone 0.5 to 1.0 mg/kg/day) produce dramatic, miraculous clinical defervescence within 24 to 48 hours, followed by rapid clearing of cutaneous plaques over 1 to 2 weeks. Tapered over 4 to 6 weeks to prevent relapse.
• Steroid-Sparing First-Line Alternatives:
  • Potassium Iodide (SSKI): 300 mg three times daily (inhibits neutrophil chemotaxis).
  • Colchicine: 0.5 mg twice or three times daily.
  • Dapsone: 100 to 150 mg daily (check G6PD prior to therapy).
  • Indomethacin: 50 mg three times daily.