The term seronegative myasthenia gravis (SNMG) refers to the generalized disease without detectable anti‐acetylcholine receptor (anti‐AChR) antibodies. In these patients, IgG antibodies against the muscle‐specific kinase (MuSK) have been described, which reduced agrin‐induced AChR clustering in vitro. We have assayed anti‐MuSK antibodies in 78 patients with SNMG, who have been followed for many years in our Institution. Here we describe the clinical phenotype of the 37 patients whose results were positive on this assay. MG with anti‐MuSK antibodies was characterized by a striking prevalence of female patients (eight men and 29 women). Age of onset ranged from 6 to 68 years, with 56.8% of patients presenting under 40 years of age. All these patients shared a similar pattern of muscle weakness, with prevalent involvement of cranial and bulbar muscles and a high frequency of respiratory crises; the involvement of limb muscles was comparatively less severe and inconsistent. Single‐fibre‐EMG confirmed the most sensitive examination in the EMG diagnosis of MuSK‐positive disease, while, owing to weakness topography, repetitive nerve stimulation in limb muscles was diagnostic in 56.8% of cases. The effect of edrophonium (or neostigmine) injection was equivocal or negative in 11 of 37 patients (29.7%), and the response to oral pyridostigmine was even more unsatisfactory, ranging from mild benefit to overt intolerance. In thymectomized patients, thymus was normal for age or atrophied, and no benefit from surgery was noticed. Thirty‐five of 37 patients were given immunosuppressive therapy and 22 received plasma‐exchange. The course of the disease was often characterized by periodic exacerbation phases requiring hospitalization and even assisted ventilation; plasma‐exchange produced marked improvement in these cases. At the end of the observation period, most patients, although improved, were still symptomatic, having developed permanent facial and pharyngeal weakness together with some atrophy of facial muscles. MuSK‐negative disease was comparatively more heterogeneous. Most patients were affected with mild to moderate symptoms and responded well to pharmacological treatment; however, a few subjects in this group had severe refractory disease, poorly responsive to both acetylcholinesterase inhibitors and immunosuppressants.

Calprotectin (CLP) is a calcium-binding protein produced by neutrophils and monocytes in the course of inflammation. Today, the role of faecal CLP in chronic IBD is well known, but in recent years attention has shifted towards circulating CLP. In fact, this molecule can be measured in different biological fluids: blood, saliva and urine, using different analytic methods that are described in this review. Furthermore, different data confirm the relevant role of serum CLP in autoimmune diseases. In this review we will highlight the correlation between high levels of circulating CLP and specific autoantibodies of major autoimmune pathologies paving the way to the employment of CLP measurement as useful biomarker for monitoring outcome in different pathologies.