Mevalonate kinase deficiency (MKD), also known as Hyper IgD syndrome, is an inborn error of metabolism characterized by inflammatory dysregulation and, in most severe cases, neurodevelopmental delay. The clinical phenotype of each patient depends on the severity of the underlying enzymatic defect and on environmental factors. Due to its complex pathogenesis, involving both metabolic and immune functions, the disease shows different clinical pictures mimicking infectious, inflammatory, rheumatologic and neurological disorders. In these cases the correct diagnosis may be delayed and the patient may undergo useless investigation and treatment. In the present work five common patterns of clinical presentation of the disease that can lead to a late or wrong diagnosis are identified. Considering MKD as a novel “great mimicker” can foster awareness of this disorder among paediatricians and physicians in different medical specialties. Each case will enable to discuss possible diagnostic pitfalls and to propose practical hints to improve the diagnosis.
