Sir,

A 78-year-old woman was referred to our hospital, complaining of itchy erythematous eruption on the trunk and extremities one week previously. She did not have any contributory medical histories. On physical examination, the upper abdomen, axilla, and lower extremities had multiple palpable purpuric plaques, some of which presented with an annular appearance (Figs. 1a and 1b). Laboratory examination showed normal levels of leukocytes (5300 μ/L) with normal fractions, and C-reactive proteins, and kidney and liver functions were normal. Antinuclear antibodies were positive (1:320, homogeneous), whereas anti-DNA, anti-dsDNA, anti-ssDNA, anti-cardiolipin β2GP1, anti-RNP, anti-SS-A, and anti-SS-B antibodies were all negative. Serum IgG (2379 mg/dL, normal: 861-1747) and IgG4 (493 mg/dL, normal: 11-121) levels were increased, and hypocomplementemia was observed (CH50: 12.0 U/mL (normal: 25-48), C3: 51 mg/dL (normal: 73-138), C4: 3 mg/dL (normal: 11-31), and C1q: 5.2 mg/dL (normal: 8.8-15.3)), and the level of C1q immune complexes was decreased (3.5 μg/mL, normal<3). Histopathological findings showed infiltration of neutrophils, nuclear dusts, and extravascular leakage of erythrocytes in the perivascular area of the upper dermis, whereas fibrinoid necrosis was not prominent and plasma cell infiltration was not observed (Fig. 2). Direct immunofluorescence did not reveal deposition of IgG, IgG4, IgA, IgM, C3, and C1q in the vessel walls. Computed tomography showed lymphadenopathies in both groins and axillae and thyromegaly, but there were no clear interstitial changes, retroperitoneal fibrosis, or findings suspicious of an inflammatory aortic aneurysm. The purpura had almost disappeared spontaneously 2 weeks later, and no recurrence was observed.

	Figure 1: Annular purpuric lesions of the lower extremities (a,b).
	Figure 2: Histopathological examination showing infiltration of neutrophils, nuclear dusts, and extravascular leakage of erythrocytes in the upper dermis (H-E stain, original magnification ×200).

The present case developed annular urticarial vasculitis with hypocomplementemia. She had positive anti-nuclear antibodies but did not fulfill the criteria of either systemic lupus erythematosus or Sjögren’s syndrome. She developed multiple lymphadenopathies and thyromegaly, with elevated serum IgG4, and thus considered as a possible IgG4-related disease (IgG4-RD) according to the comprehensive diagnostic criteria [1,2]. Because superficial lymphadenopathies were not observed, biopsy was not performed in the present case. To date, there are only a few papers of hypocomplementemic urticarial vasculitis (HUV) in patients with either IgG4-RD [3] or elevated serum IgG4 levels [4]. A previous case showed leukocytoclastic vasculitis in a patient with hypocomplementemic urticarial vasculitis syndrome [4], which is characterized by urticarial vasculitis, persistent hypocomplementemia and several systemic disorders present over 6 months. By contrast, our patient developed transient urticarial vasculitis, without extracutaneous manifestations such as fever, malaise, fatigue, arthralgia, myalgia, as well as other organ involvement. Because biopsy specimen taken from urticarial rash did not show infiltration of plasma cells, skin manifestation of the present case was not specific sign of IgG4-RD, which showed elevated IgG4-positive cell counts and IgG4/IgG ratio [5].

It was reported that 30-40% of patients with IgG4-RD have hypocomplementemia [3], but rarely develop hypocomplementemic leukocytoclastic vasculitis [6]. Although IgG4 has no or little ability to activate complement, IgG4 can stimulate neutrophils via Fc receptors to lead to vasculitis [7]. Alternatively, IgG4 does not play a direct role in HUV, but HUV may be included as one of the secondary eruptions associated with IgG4-RD. In conclusion, our case suggests that HUV may occur in patients with possible IgG4-RD. Our patient is under careful follow-up whether she develop any systemic disorders.

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