Sufficient pressure for a sufficient period of time can cause hair loss with alopecia.
(1) There is a history of a preceding event within the past month with the head in a fixed position:
(1a) prolonged general anesthesia
(1c) following trauma
(2) There is a loss of hair after the event in the area of the head under pressure, typically the occipital region. There is a fairly sharp demarcation between the area of alopecia and the surrounding hair.
(3) The alopecia may be unexpected based on age, gender or distribution.
Histologic findings of a biopsy taken in the affected area may include:
(1) Vascular thrombosis may be present (which may correlate with a hypercoagulable state).
(2) Fat or ischemic necrosis may be present.
(3) There is low-grade chronic perivascular, perifollicular and dermal inflammation.
(4) Trichomalacia may be present.
(5) Terminal hairs are predominantly in the telogen or catagen phase (synchronized conversion).
(6) Pigment casts may be seen in the hair follicle.
(1) In most cases the hair regrows.
(2) If sufficient necrosis and scarring occur then cicatricial alopecia may follow.
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