Laboratory Studies
The most important goal is to differentiate black heel (calcaneal petechiae) from melanoma. No specific workup is necessary to make the diagnosis of black heel.
Imaging Studies
Epiluminescence techniques, such as dermatoscopy and video macroscopy, can be used to aid in the differentiation of melanoma from black heel. [10, 11] Under the dermatoscope, black-reddish globules on the ridges (resembling pebbles) are characteristic. [12] If doubt persists, rapidly process the shaved fragments of keratin with commonly available screening tests used for detection of occult blood.
Procedures
The diagnosis of black heel (calcaneal petechiae) is clinical and can be aided by paring down the lesion with a surgical blade. Melanocytic lesions do not lose their pigmentation with paring, while black heel may clear completely after the stratum corneum is removed.
A biopsy is indicated if the diagnosis remains in doubt, but this is seldom necessary.
Histologic Findings
Hyperkeratotic stratum corneum typical of acral skin is seen; parakeratosis is common. Extravasated erythrocytes in the dermal papillae are characteristic. Often, biopsy is only performed to the stratum corneum and the hemorrhage can be identified as loculated serum and degenerated erythrocytes. [13]
Phagocytosis of extravascular RBCs and subsequent degradation of hemoglobin to hemosiderin does not occur; therefore, traditional iron stains do not work and histochemical stains must be directed toward hemoglobin. Benzidine stain reveals brown homogenous clusters of hemoglobin. [14, 15]
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Linear petechiae on the heel, characteristic of black heel.
