bubble_chart Overview

This disease is a tropical pestilence. Its clinical manifestations resemble syphilis, but it is not a sexually transmitted disease and is not hereditary. It primarily affects the skin without invading vital internal organs or the central nervous system, though advanced stages may involve the bones. It is more commonly seen in young adults and children. The disease is prevalent in tropical regions such as Central Africa, South Asia, and South America. A few cases have been reported in southern China, but it has now largely disappeared.

bubble_chart Etiology

The disease is caused by the invasion of Treponema pertenue through breaks in the epidermis. The morphology of Treponema pertenue is similar to that of syphilis spirochetes, but its virulence is weaker. The main route of infection is close contact, transmitted through broken skin. Early symptoms primarily involve skin lesions, such as papules, pustules, granulomatous or gummatous destruction, while bone yaws is a manifestation of its late stage (third stage). The incidence rate in China is approximately 4.5% to 6.5% of yaws cases, with some reports indicating about 10-20% of patients developing bone and joint complications.

bubble_chart Pathological Changes

The pathological changes primarily involve the proliferation of fibrous tissue between bone trabeculae, extensive necrosis of periosteal tissues, with the necrotic tissue surrounded by markedly proliferated fibrous tissue, infiltrated by lymphocytes, polymorphonuclear neutrophils, and plasma cells, forming a gumma-like morphology. Bone lesions are mostly located in the tibia and fibula, ulna and radius, and humerus, but the frontal bone, mandible, femur, metacarpals, scapula, and ribs may also be affected. Multiple bones can be involved in the same patient. The forms of lesions may include periostitis, osteitis, or osteomyelitis. Periostitis mainly manifests as hyperplasia of the periosteum. Osteitis is characterized by widespread osteoporosis accompanied by multiple small round or oval areas of bone destruction and resorption. Some cases of destruction are severe enough to cause pathological fractures. When joints are affected, the elbow, hip, and sacroiliac joints are commonly involved. Occasionally, perforation of the palate and destruction of the nasal bones may occur.

bubble_chart Clinical Manifestations

Among family members, due to close contact, there is often a history of mutual pestilence. Its clinical symptoms and manifestations are similar to syphilis and can be divided into the late stage [third stage]:

1. The initial stage [first stage] is called the mother yaws period. The disease occurs 2–3 weeks after infection, with small red papules appearing at the site of skin contact, which may then develop into ulcers of varying numbers, raised about 2–3 cm above the skin surface and 1–10 cm in diameter. The base consists of granulation tissue resembling Chinese wax myrtle bark, firm to the touch like rubber but prone to bleeding, with significant serous exudation that may crust over. The surrounding area shows erythema and generally heals spontaneously in about 2–3 months. Local lymph nodes may swell, but bones and joints are not affected.

2. The intermediate stage [second stage] is called the yaws rash period. Within 1–3 months after the early rash appears, symptoms such as generalized joint pain, fever, and headache may occur. This is the systemic infection phase, with generalized lymphadenopathy, though the patient’s overall condition remains relatively stable. Skin lesions are mostly ulcerative papules, which can exceed 10 cm in diameter and leave scars after healing. These lesions predominantly appear on exposed areas such as the face, limbs, and buttocks in children, while the perineum is rarely affected. Mucous membranes are usually spared. Skin lesions may persist for several months to 2–3 years. During this stage, bones may be affected, presenting as periostitis and bony protuberance changes, primarily involving bone hyperplasia, which can affect the entire shaft. Subperiosteal new bone formation leads to shaft thickening, and widespread periosteal changes are typical in the intermediate stage [second stage] of yaws.

3. The late stage [third stage] is called nodular ulcerative yaws or advanced-stage yaws, usually occurring 6–10 years after infection. Most yaws cases terminate at the intermediate stage [second stage], with progression to the late stage [third stage] being less common. About 10–20% of late-stage cases involve bone and joint complications. The main manifestations include enlarged and deepened ulcers with underlying bone destruction. When the outer edge of the cortical bone is damaged, the margins show irregular bone defects; if the inner edge is affected, multiple cystic radiolucent areas with reduced bone density appear, accompanied by surrounding bone hyperplasia, while periosteal reactions are mild or absent. The more pronounced the local ulcer, the more severe the bone destruction. In the skull, lesions often present as cystic destruction surrounded by sclerotic bone. In the tibia, bone hyperplasia and periosteal proliferation dominate, accompanied by medullary cavity narrowing, giving a "saber shin" appearance.

bubble_chart Auxiliary Examination

A large number of yaws spirochetes can be found in the smear of ulcer exudate. It is often difficult to find them in pathological sections of bone lesions. The serum Wassermann reactions of yaws patients are all positive or strongly positive, but the Wassermann reactions of cerebrospinal fluid are all negative, indicating that the spirochetes do not invade the central nervous system.

bubble_chart Diagnosis

During diagnosis, it is essential to thoroughly understand the medical history and carefully observe and analyze clinical manifestations. The detection of yaws spirochetes in smears of ulcer exudate confirms the diagnosis.

bubble_chart Treatment Measures

The primary approach is systemic treatment. The main drug is procaine penicillin, with some advocating a total dosage of 6 million units. The first intramuscular injection is 300,000 units, followed by 600,000 units per dose, administered twice daily via intramuscular injection.

Symptomatic treatment can be applied locally to the affected limb. This includes timely cleaning and dressing changes, as well as temporary immobilization of the limb using an external fixation brace to achieve limb stabilization and pain relief. Generally, after treatment during the active phase, bone lesions may disappear. In mild cases, X-rays may show normal bone structure, while severe cases may leave behind bone deformities and hyperostosis or sclerosis. Pain typically subsides rapidly.

bubble_chart Differentiation

In differential diagnosis, special attention should be paid to distinguishing it from bone syphilis. Both are pestilence diseases caused by spirochetes and exhibit similar manifestations in skin lesions and bone lesions. Serum Kahn and Wassermann reactions are both positive. However, careful analysis of their respective characteristics reveals differences: yaws is more common in young people and children, while syphilis is more prevalent in infants and adults; yaws patients and their parents have no history of sexually transmitted diseases, only a history of contact with pestilence and residence in endemic areas, whereas syphilis patients and their parents differ. The lesions also differ: in syphilis, the initial stage [first stage] chancre is often located on the external genitalia, whereas yaws rarely affects the external genitalia, and mucous membranes are usually unaffected. In the intermediate stage [second stage] of syphilis, biopsies show small vessel endarteritis, which is absent in yaws. The bone lesions of syphilis are characterized primarily by periosteal hyperplasia, with relatively less bone destruction.