STEPTRACKERCARDIOVASCULAR | PATHOLOGY + IMMUNOLOGY | HIGH-YIELD REVIEW

Small-Vessel Vasculitis — Immune Complex

IgA vasculitis, cryoglobulinemic vasculitis, cutaneous leukocytoclastic vasculitis and Behçet disease — palpable purpura is the calling card.

FOCUS ON
Palpable purpura with a normal platelet count means small-vessel vasculitis. IgA vasculitis is the child after a URI (purpura, joints, belly, kidney). Cryoglobulinemia means HCV and low C4. Behçet means oral and genital ulcers plus uveitis.
DISEASE
MECHANISM · PATHOLOGY
FEATURES
CLUE · TREATMENT
IgA vasculitis
Henoch-Schönlein purpura
Galactose-deficient IgA1 immune complexes deposit in small vessels of skin, gut, kidney, joints.
Child after a URI: palpable purpura on buttocks and legs, arthralgia, colicky abdominal pain, hematuria
Most common childhood vasculitis; risk of intussusception · supportive, steroids if severe
Cryoglobulinemic vasculitis
Immunoglobulins that precipitate in the cold (mixed: monoclonal IgM with RF activity + polyclonal IgG) → complement consumption.
Purpura, arthralgia, weakness; Raynaud; neuropathy; membranoproliferative GN
HCV is the usual cause; ↓ C4 · treat HCV
Cutaneous leukocytoclastic vasculitis
hypersensitivity
Drug or infection antigens form complexes in postcapillary venules.
Palpable purpura limited to skin (legs), 1–2 weeks after a new drug
Leukocytoclasis (neutrophil nuclear dust) · stop the drug
Behçet disease
variable vessel size
Neutrophilic vasculitis; HLA-B51; Silk Road region (Turkey, Middle East, East Asia).
Recurrent painful oral aphthae + genital ulcers + uveitis; erythema nodosum; arterial and venous thrombosis
Pathergy (pustule at needle stick) · colchicine, apremilast, steroids
Anti-GBM disease
small vessels, type II
Antibodies to α3 chain of type IV collagen in lung and kidney basement membranes.
Hemoptysis + RPGN
Linear IgG on immunofluorescence — page 12.07
SLE / RA vasculitis
Immune complexes from the underlying disease.
Purpura, digital infarcts, mononeuritis
Low complement in SLE
Palpable vs flat purpura
Inflamed vessel wall leaks RBCs into a raised lesion; platelet problems give flat bleeds.
Palpable purpura = vasculitis · petechiae/ecchymoses = platelets or coagulation
Check the platelet count

Mechanism — leukocytoclastic vasculitis

AntigenPost-infection IgA, HCV cryoglobulins, drug
→
Immune complexesLodge in venules
→
ComplementNeutrophils recruited
→
Vessel wall necrosisNuclear dust
→
RBCs leakPalpable purpura

Telling them apart

DISEASE
KIDNEY
COMPLEMENT
KEY TEST
IgA vasculitis
IgA nephropathy-like GN
Normal
IgA in vessels on skin biopsy
Cryoglobulinemic
MPGN
↓ C4
Cryoglobulins; HCV RNA
Leukocytoclastic
Rare
Normal
Drug history; skin biopsy
Behçet
Rare
Normal
Pathergy, HLA-B51

How it's tested

COMMON CONFUSIONIgA vasculitis and IgA nephropathy share the same IgA immune-complex kidney lesion. HSP adds skin, gut and joint disease.
THE TRAPA child with IgA vasculitis develops severe colicky pain and currant-jelly stool. Vasculitis of the bowel wall has caused an intussusception, which needs urgent reduction.
YOUR APPROACHPurpura + normal platelets → vasculitis → age, infection, drugs, ulcers → check complement and HCV.

If you see… think…

Child after a URI: buttock purpura, joint pain, belly pain, hematuria → IgA vasculitis
HSP child with currant-jelly stool → intussusception
HCV + purpura + arthralgia + weakness + low C4 → mixed cryoglobulinemia
Membranoproliferative GN in an HCV patient → cryoglobulin deposits
Leg purpura 10 days after starting an antibiotic → leukocytoclastic vasculitis
Recurrent oral + genital ulcers + uveitis → Behçet disease
Sterile pustule where blood was drawn → pathergy (Behçet)
Palpable purpura with normal platelets → small-vessel vasculitis
Flat petechiae with platelets 15,000 → thrombocytopenia, not vasculitis