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Imaging Diagnosis

The only significant radiological findings in yaws and nonvenereal syphilis occur in the skeleton. The soft tissue deformities and skin lesions seen in these diseases may be striking and often help to establish the diagnosis, but they seldom result in significant imaging findings. Skeletal lesions may occur at any time during the secondary and tertiary stages, but there is no practical reason for the radiologist to classify the roentgen changes in terms of the stage of the clinical lesions. The radiographic appearances of the skeletal lesions are so similar in the second and third stages and are so frequently altered by secondary infection or prior treatment that such a categorization may be impossible in the individual case.

The radiological pattern of yaws in both the secondary and tertiary stages reflects the underlying pathological changes and is basically that of a marked osteomyelitis and accompanying periostitis (Fig. 35.4). The softening of the bones, due to osteoporosis and bone destruction during the active phase of the disease, causes morphological changes and deformities in the limb bones. Almost any bone may be involved (except perhaps the distal phalanges), but the lesions tend to be most common in the forearms, hands, legs, and feet, and less frequent in the skull, facial bones, spine, and peripheral joints. They are frequently bilateral and tend to be symmetrical, but may involve different bones in different limbs. Dactylitis in both hands and feet is usually seen in the secondary stage, but it may be impossible to distinguish between the second and third stages radiologically. Computed tomography (CT) may be helpful in a few cases, especially to demonstrate the pathological anatomy before surgery, but it seldom adds really useful diagnostic information.

The earliest bony change seen in the active phase of yaws is a generalized osteoporosis of the involved bone, which rapidly becomes more focal and intense and is followed by the appearance of multiple, tiny, localized lytic areas in the cortex and medulla ("borer beetle" appearance). These lytic foci expand and coalesce from their original size of a few millimeters, to reach 2 cm or more in diameter. The lesions at this stage are discrete with relatively sharp margins, although there is usually little or no surrounding sclerosis. No sequestra are present.

Associated with these cortical and medullary changes is an exuberant periosteal reaction (Figs. 35.4 & 35.5), which may be even more striking than the underlying lysis of bone. It is characteristically linear or lamellar in the early stages and is more marked in the area immediately overlying the foci of bone destruction (this is the phase of "osteoperiostitis"). This periosteal reaction typically surrounds the entire shaft of the affected bone and, within a week, is incorporated into the original cortex. In some cases the prolific periosteal reaction may progress until it becomes an organized fusiform mass, resembling a tumor. This "mass" may be clinically palpable, and may be the reason why the patient eventually seeks medical attention.

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Fig. 35.4A-H. Treponemal bone infection in the hands and feet of children. A, B There are lytic foci surrounded by an exuberant, coarse lamellar periosteal reaction on many of the phalanges and metacarpals, particularly the first and fifth of the left hand. This is the phase of osteoperiostitis. C,D Two different images of an older child (right foot) in whom the periosteal reaction has become incorporated into the cortex: the lytic foci have almost disappeared. There is quite marked widening of the proximal phalanges of the second to fifth toes due to periosteal thickening. This degree of thickening can be felt clinically. E In this child the third metatarsal has lost its normal shape because of the periosteal reaction. There are less marked changes on the second and fourth metatarsals. There are still a few residual lytic foci, particularly at the proximal end of the fifth metatarsal. F The left hand of a child showing a similar reaction in some of the phalanges and metacarpals, while others seem to be normal. There are lytic foci and a periosteal reaction in the lower end of the ulna. G, H Yaws in a 15-year-old girl from Indonesia. The diagnosis was made clinically and confirmed by positive serology. She came from a remote rural region and syphilis was considered very unlikely. G Tender swelling of both middle fingers: the presenting complaint of the child. She was otherwise in good health. H There is a marked thick periosteal reaction around the proximal phalanges of both middle fingers. Radiographs of both lower legs showed less marked, probably older, reaction with a patchy distribution. (Courtesy of Dr. H. J. Engelkens et al. and Skeletal Radiol, 1992).

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Fig. 35.5 A-C. The early periosteal reaction of treponemal infections: A around the lower end of the femur; B on the lower tibia and fibula; C in the lower leg of a different patient. This feathery periosteal reaction can occur without any underlying bone lesion, although there is often some osteoporosis. The reaction is nearly always irregular and spreads along the bone. In the lower leg, similar periosteal changes can occur when there is prolonged edema, as in filariasis or with varicose veins.

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