Multiple sclerosis (MS) and necrotizing periodontitis (NP) are two diseases whose aetiology and pathophysiology do not seem to have a common link; however, the treatment of MS with monoclonal antibodies and the decrease in humoral immunity that this entails can be a trigger or an aggravation in patients who present NP. We present a clinical case of NP in which its clinical manifestations, treatment and evolution during therapy with ocrelizumab are reflected. During the evolution of the case, a rapid progression of NP was evidenced. During her evolution, the patient suffered bilateral pneumonia due to COVID requiring treatment with corticosteroids and antibiotics, which led to clinical relief of her NP. Given this important clinical finding, we consider of great interest the regulated dental monitoring of those patients with MS before, during and after the administration of monoclonal antibodies to prevent periodontal deterioration.