Objective: Rare disease Background: Pyoderma gangrenosum is a rare, ulcerative cutaneous condition that was first described by Brocq in 1916. This diagnosis is quite challenging as the histopathological findings are nonspecific. Pyoderma gangrenosum is usually associated with inflammatory bowel disease, leukemia, and hepatitis C. We describe a rare clinical case of a patient with hepatitis C (HCV), mixed cryoglubinemia, and pyoderma gangrenosum, which was successfully treated with prednisone in combination with the new antiviral medication ledipasvir/sofosbuvir. Case Report: A 68-year-old male with a history of untreated HCV presented to the clinic with a left lower extremity ulcer that had progressively worsened over 4 days after the patient sustained a minor trauma to the left lower extremity. Examination revealed a 2×3 cm purulent ulcer with an erythematous rim on medial aspect of his left lower leg. HCV viral load and genotype analysis revealed genotype 1A with polymerase chain reaction (PCR) showing viral counts of 9,506,048 and cryoglobulinemia. With a worsening and enlarging erythematous ulcer and failure of IV antibiotic therapy, the patient underwent skin biopsy, which showed acanthotic epidermis with superficial and deep perivascular lymphoplasmacytic dermatitis admixed with mild neutrophilic infiltrate. The patient was subsequently started on ledipasvir/sofosbuvir and prednisone with a high suspicion of pyoderma gangrenosum. At one-month follow-up at the hepatology clinic, the patient demonstrated a near resolution of the lower extremity ulcer with undetectable viral load. Conclusions: Pyoderma gangrenosum is an inflammatory process of unknown etiology, and establishing the correct diagnosis can be a difficult task. For this reason it is prudent for clinicians to consider Pyoderma gangrenosum in their differential diagnosis, especially in the setting of a nonhealing surgical wound or skin infection.

Les vascularites cryoglobulinémiques associées au virus de l'hépatite C (VC-VHC) sont caractérisées par une expansion clonale de lymphocytes B mémoires anergiques CD27+IgM+CD21-/low (Bm21-), un défaut quantitatif en lymphocytes T régulateurs (Tregs) et une polarisation Th1. Les antiviraux d'action directe sans interferon (DAAs) sont très efficaces chez les patients VC-VHC mais leur mécanisme d'action sur l'immunité cellulaire reste inconnu. Nous montrons que les DAAs normalisent la plupart des perturbations de l'homéostasie lymphocytaire B et T, en diminuant l'expansion des Bm21- et T folliculaires, et en augmentant les T régulateurs (Tregs). Nous avons étudié l'effet des Bm21- sur les sous-populations lymphocytaires T, et les réactivités de leur récepteur B. Nous montrons que les Bm21- stimulés par le CpG favorisent la sécrétion d'IFNγ par les T effecteurs et induisent leur prolifération. Inversement, les Bm21- stimulés par CpG diminuent la capacité proliférative des Tregs. Nous montrons la diversité intraclonale des IgM mutés des Bm21-, conduite par maturation d'affinité antigène dépendante. Les anticorps (Ac) des Bm21- ont une activité facteur rhumatoïde (FR) mais ne sont ni polyréactifs, ni autoréactifs contre les autoantigènes ubiquitaires. Les Ac des Bm21- ne présentent pas de réactivité croisée contre des antigènes viraux du VHC. Les Bm21- stimulés par CpG ont une signature transcriptomique révélant un phénotype non tolérogène. Ainsi, ces résultats suggèrent le rôle majeur des Bm21- dans le défaut tolérance des patients CV-VHC, à la fois par la stimulation CpG conduisant à une réactivation des Bm21- anergiques, et par l'expression clonale des IgM à activité FR. / Hepatitis C virus-associated cryoglobulinemia vasculitis (HCV-CV) is characterized by an abnormal clonal expansion of anergic CD27+IgM+CD21-/low memory B cell (Bm21-), a quantitative defect in regulatory T cells (Tregs) and Th1 profile. Interferon-free direct-acting antivirals (DAAs) proved to be very effective in patients with HCV-CV but their mechanisms of action and their effects on cellular immunity remain poorly defined. Our results indicate that DAAs effectively normalizes many of the disturbances in peripheral B- and T-lymphocyte homeostasis of HCV-CV patients, by reducting Bm21- and T follicular helper expansion and promoting Tregs. Then, we investigated the effects of Bm21- on T-cell subpopulations and study the reactivities of their B-cell receptors. We show that CpG-stimulated Bm21- promote the secretion of IFNγ by effector T cells and induce their proliferation. Conversely, stimulated Bm21- reduce the proliferative capacity of regulatory T cells. Bm21- B-cell expansions show intraclonal diversity of highly mutated IgM antibodies that were shape by an antigen-driven maturation process. Bm21- antibodies possess rheumatoid factor activity but are neither polyreactive nor recognize ubiquitous autoantigens. No crossreactivity of Bm21- antibodies against several HCV antigens was observed. We also identify a transcriptional signature in CpG-stimulated Bm21- revealing a phenotype sufficient to break the immune tolerance. Thus, these results strongly suggest a major role for Bm21- in defective tolerance of HCV-CV patients, both through CpG stimulation leading to reactivation of anergic Bm21-, and through the clonal expression of IgM antibodies with RF activity.