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Common variable immunodeficiency (CVID) is the most prevalent primary immune deficiency, affecting roughly 2-4/100 000 individuals in the general population. The etiology is currently unknown, even if several genetic mutations have been described, and no single clinical feature or single laboratory test can establish the diagnosis, which is based on multiple criteria. CVID is characterized by B- and T-cell dysfunction that predisposes to an increased risk of infections, with the typical involvement of the respiratory and gastrointestinal tracts. Besides this well-established complication, though the coexistence of immunodeficiency and autoimmunity appears paradoxical, two-thirds of CVID patients present concomitant autoimmune disorders. Of note, autoimmunity can often be the only clinical manifestation of CVID at the time of diagnosis. The most common autoimmune disorders associated with CVID are autoimmune cytopenias, that is, immune thrombocytopenic purpura and autoimmune hemolytic anemia, either as separate entities or as concurrently (Evans syndrome). CVID patients can also manifest rheumatologic diseases (eg, arthritis, Sjogren's disease, systemic lupus erythematosus, vasculitis, Behçet's syndrome) and gastrointestinal autoimmune disorders (eg, ulcerative colitis, autoimmune atrophic gastritis, celiac disease). This latter may pose a particular diagnostic challenge, as celiac-specific autoantibodies can be absent in CVID patients. Understanding the molecular basis and the clinical impact of autoimmunity in CVID patients might help manage CVID, thus reducing its diagnostic delay and preventing its complications.

The spectrum of gluten-related disorders (GRD) has emerged as a relevant phenomenon possibly impacting on health care procedures and costs worldwide. Current classification of GRD is mainly based on their pathophysiology, and the following categories can be distinguished: immune-mediated disorders that include coeliac disease (CD), dermatitis herpetiformis (DH), and gluten ataxia (GA); allergic reactions such as wheat allergy (WA); and non-coeliac gluten sensitivity (NCGS), a condition characterized by both gastrointestinal and extra-intestinal symptoms subjectively believed to be induced by the ingestion of gluten/wheat that has recently gained popularity. Although CD, DH, and WA are well-defined clinical entities, whose diagnosis is based on specific diagnostic criteria, a diagnosis of NCGS may on the contrary be considered only after the exclusion of other organic disorders. Neither allergic nor autoimmune mechanisms have been found to be involved in NCGS. Mistakes in the diagnosis of GRD are still a relevant clinical problem that may result in overtreatment of patients being unnecessary started on a gluten-free diet and waste of health-care resources. On the basis of our clinical experience and literature, we aim to identify the main pitfalls in the diagnosis of CD and its complications, DH, and WA. We provide a practical methodological approach to guide clinicians on how to recognize and avoid them.