Split fingernails, underdeveloped thumbnails, and triangular lunulae

A 67-year-old man presented to the dermatology clinic for evaluation of split nails. His medical history was notable for bilateral elbow surgeries. On physical examination, it was noted that the patient had split nails of his index fingernails and underdevelopment of his thumbnails (Fig 1). All his fingernails, except for the thumbnails, had triangular lunulae.