A raised central portion of the nail is a change in the shape of the nail due to damage to the nail plate and sub nail tissue, manifested by the central portion of the nail protruding above the rest of the nail plane.
Causes include trauma, infection, drug factors, environmental factors, poor lifestyle, associated skin diseases (e.g. nail lichen planus, chronic eczema, pemphigus, follicular keratosis, sub nail tumours) and systemic diseases such as rheumatoid arthritis.