Acro-Osteolysis: A condition with congenital and acquired forms causing recurrent ulcers in the fingers and toes. The congenital form exhibits autosomal dominant inheritance; the acquired form is found in workers who handle VINYL CHLORIDE. When acro-osteolysis is accompanied by generalized OSTEOPOROSIS and skull deformations, it is called HAJDU-CHENEY SYNDROME.Hajdu-Cheney Syndrome: Rare, autosomal dominant syndrome characterized by ACRO-OSTEOLYSIS, generalized OSTEOPOROSIS, and skull deformations.Mononeuropathies: Disease or trauma involving a single peripheral nerve in isolation, or out of proportion to evidence of diffuse peripheral nerve dysfunction. Mononeuropathy multiplex refers to a condition characterized by multiple isolated nerve injuries. Mononeuropathies may result from a wide variety of causes, including ISCHEMIA; traumatic injury; compression; CONNECTIVE TISSUE DISEASES; CUMULATIVE TRAUMA DISORDERS; and other conditions.