Yaws Workup

Updated: Oct 25, 2021
  • Author: Hassan I Galadari, MD; Chief Editor: William D James, MD  more...
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Approach Considerations

The diagnosis of yaws is made by clinical evaluation of lesions and is confirmed by the detection of treponemes on dark-field microscopy of serum obtained by squeezing the bases of the lesions.

Radiologic studies are nonspecific but can include any of the following findings:

  • Surface striations (periostitis)

  • Cortical thickening with bowing (saber shin deformity)

  • Spiculated periosteal reaction

  • General osseous expansion

  • Gummatous destruction

  • Draining sinuses

  • Epiphyseal separation

  • Stellate frontal bone scans


Serologic Tests

Serologic tests for yaws are identical to those for venereal syphilis, including rapid plasma reagent (RPR) test, Venereal Disease Research Laboratory (VDRL) test, fluorescent treponemal antibody absorption (FTA-ABS) test, T pallidum immobilization (TPI) test, and T pallidum hemagglutination assay (TPHA). RPR and VDRL tests are reactive 2-3 weeks after the onset of the primary lesion, and they generally remain reactive throughout all stages.

No serologic test can distinguish yaws from other nonvenereal treponematoses; therefore, diagnosis is ultimately based on correlation of the clinical findings, epidemiologic history, and positive serologic results that are suggestive of yaws. Biopsy of late lesions may be needed to show characteristic histopathology. [18]


Histologic Findings

Histologic findings in early yaws include acanthosis, papillomatosis, and spongiosis. Treponemes are found in the epidermidis. Neutrophilic exocytosis with intraepidermal microabscess formation is the most characteristic finding. The dermis has a moderate to dense granulomatous infiltrate that is mainly composed of plasma cells and lymphocytes, with few histiocytes, neutrophils, and eosinophils. Unlike syphilis, endothelial proliferation is absent or low.

Late yaws has histologic findings similar to those of tertiary syphilis, including an intense dermal infiltrate composed of epithelioid cells, giant cells, lymphocytes, and fibroblasts. Caseation necrosis can also be observed. Plasma cells and histiocytes, in contrast to early yaws, are scarce.

Silver stains (Steiner) can be used to identify numerous treponemes between keratinocytes in early yaws. They are seen in a bandlike pattern or in clusters in the epidermis. Unlike T pallidum, which is found in both the epidermis and the dermis, T pallidumpertenue is almost entirely epidermotropic.

Electron microscopy of early lesions demonstrates scarce treponemes in clusters in the intercellular spaces of the epidermis among inflammatory cells, within the cytoplasm of macrophages, and in the dermis.