This is a report presenting the unusual case of hair casts occurring after psychological trauma. These pseudonits must be correctly differentiated from pediculosis capitis.
Hair casts (peripilar keratin casts), or pseudonits, are 2 to 7 mm long, discrete, firm, shiny, white, freely movable tubular accretions that encircle the hair shafts of the scalp. Cursory examination of the patient with these pseudonits may result in the erroneous diagnosis of pediculosis capitis.
Since their original description by Kligman in 1957, more than thirty cases of hair casts have been reported in the English language medical literature. Hair casts have been classified into parakeratotic (“secondary”) or nonparakeratotic (“idiopathic”) types. The former is more common and is related to a coexistent abnormality involving the scalp, such as psoriasis. The “idiopathic” hair cast, however, is not found in association with any disease of the scalp or any other hair shaft abnormality.
Light microscopic and ultra structural studies of the nonparakeratotic hair casts demonstrate both inner and outer root sheath components and suggested an infrainfundibular origin. The exact mechanism of hair cast shedding has not, however, been elucidated.
We present an unusual case of hair casts that occurred following severe emotional trauma associated with the unexpected death of a patient’s parent. This observation suggests a possible causative basis similar to that of Beau’s lines of the nail plate.
A 9-year-old white girl was referred by her school nurse for suspected pediculosis capitis. Initial observation revealed a healthy-appearing girl with shoulder-length hair containing small white specks all located approximately 3 mm from the scalp. The scalp appeared normal. Pulling the hair did not cause increased hair shedding. Alopecia was not present and regional hairs were all of similar length. Microscopic examination of plucked hair showed tubular accretions or pseudonits but true nits were not seen.
The patient denied any recent illness, but had been distraught over the untimely death of her father thirty days earlier. She was not taking any medication. Family members were unaffected. The hair casts were removed by acetic acid soaks followed by combing; they did not recur.
Hair casts may occur in association with parakeratotic scalp disease or as an idiopathic condition apparently unrelated to other scalp and hair shaft abnormalities. Our patient had no evidence of other dermatologic disease and was not taking any medication. The onset of her hair casts appears temporally related to the severe psychological stress caused by her father’s untimely death.
Nail plate and hair abnormalities are known to occur after severe systemic insults, including psychological disturbances. After such insult, matrix mitotic activity may slow, resulting in transverse depressions of the nail plate (Beau’s lines) or focal narrowing of the hair shaft (Pohl-Pincus marks). The overall growth rate and pattern remain normal.
It seems reasonable that a similar process, affecting the process of keratinization at or just below the pilar infundibulum, could result in the formation of hair casts. The hair casts would then proceed distally, with normal hair growth, at a relatively uniform pace.
As is often the case, hair casts may initially be misdiagnosed as the nits of pediculosis capitis. Reassurance and simple mechanical removal usually suffice as treatment. While the exact mechanism of hair cast formation remains to be determined, their apparent temporal relation to severe emotional trauma suggests a causative mechanism analogous to that responsible for Beau’s lines and Pohl-Pincus marks.
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