Evanescent periostitis is met with in acquired syphilis during the period of the early skin eruptions.  The patient complains, especially at night, of pains over the frontal bone, ribs, sternum, tibiae, or ulnae.  Localised tenderness is elicited on pressure, and there is slight swelling, which, however, rarely amounts to what may be described as a periosteal node.

In the later stages of acquired syphilis, gummatous periostitis and osteomyelitis occur, and are characterised by the formation in the periosteum and marrow of circumscribed gummata or of a diffuse gummatous infiltration.  The framework of the bone is rarefied in the area immediately involved, and sclerosed in the parts beyond.  If the gummatous tissue degenerates and breaks down, and especially if the overlying skin is perforated and septic infection is superadded, the bone disintegrates and exhibits the condition known as syphilitic caries; sometimes a portion of bone has its blood supply so far interfered with that it dies—­syphilitic necrosis.  Syphilitic sequestra are heavier and denser than normal bone, because sclerosis usually precedes death of the bone.  The bones especially affected by gummatous disease are:  the skull, the septum of the nose, the nasal bones, palate, sternum, femur, tibia, and the bones of the forearm.

In the bones of the skull, gummata may form in the peri-cranium, diploe, or dura mater.  An isolated gumma forms a firm elastic swelling, shading off into the surroundings.  In the macerated bone there is a depression or an actual perforation of the calvaria; multiple gummata tend to fuse with one another at their margins, giving the appearance of a combination of circles:  these sometimes surround an area of bone and cut it off from its blood supply (Fig. 130).  If the overlying skin is destroyed and septic infection superadded, such an isolated area of bone is apt to die and furnish a sequestrum; the separation of the dead bone is extremely slow, partly from the want of vascularity in the sclerosed bone round about, and partly from the density of the sequestrum.  In exceptional cases the necrosis involves the entire vertical plate of the frontal bone.  Pus is formed between the bone and the dura (suppurative pachymeningitis), and this may be followed by cerebral abscess or by pyaemia.  Gummatous disease in the wall of the orbit may cause displacement of the eye and paralysis of the ocular muscles.

[Illustration:  FIG. 130.—­Syphilitic Disease of Skull, showing a sequestrum in process of separation.]

On the inner surface of the skull, the formation of gummatous tissue may cause pressure on the brain and give rise to intense pain in the head, Jacksonian epilepsy, or paralysis, the symptoms varying with the seat and extent of the disease.  The cranial nerves may be pressed upon at the base, especially at their points of exit, and this gives rise to symptoms of irritation or paralysis in the area of distribution of the nerves affected.