Corns under the nail, or medically referred to as subungual keratomas, develop not dissimilar to other identified corns. There is excessive pressure borne on the nail bed resulting in thickening and keratinizing of the nail bed epithelium or skin. These are challenging to eliminate as they are protected by the overlying nail plate. Frequently, a portion of the nail may need to be removed to gain access. This may be done under local anesthesia if it is too sensitive to be done without anesthetic. As this is not a frequent area to develop these lesions due to protection from the nail plate, it may be wise to biopsy the presentation if there is any suspicion that this is not keratinized skin (abnormal coloration, irregular borders, altered appearance of the surrounding nail bed skin, etc.). If there is any appreciation or local deformity, it may be wise to also obtain an X-ray to rule out a not uncommon bone growth or exostosis that develops on the distal phalanx that can contribute to these lesions (subungual exostosis or osteochondroma). If this is present, the bone enlargement may also need to
be reduced and biopsied.