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pseudonits

Pseudonits

Pseudonits also called hair casts, peripilar keratin casts or peripillous sheaths, are small movable white-to-yellow tubular or or nodular structures that encircle the proximal hair shafts of the scalp 1. Pseudonits consist of hyperkeratotic or parakeratotic cells from both the internal and the external epithelial sheaths of the hair root, that surround the hair shafts 2. Varying in length (2–7 mm), pseudonits slide easily along the shaft without breaking it 3. The fact that hair casts easily slide along the shafts helps in differentiating them from other disorders of the scalp such as pediculosis capitis, piedra, trichomycosis, trichonodosis, and trichorrhexis nodosa 4. Hair cast pseudonits often get misdiagnosed as pediculosis capitis; however, the latter is symptomatic 5. Pseudonits hair casts usually involve only scalp hair. However, hair casts are known to involve beard, chest, axillary, and pubic hair 6.

Kligman, in the year 1957 for the first time, used the term hair casts in his article “parakeratotic comedones of scalp” 7. Hair casts pseudonits are classified as primary (idiopathic or nonparakeratotic peripilar) casts when there is no associated scalp condition, and as secondary (parakeratotic casts) when associated with scaling scalp conditions such as seborrheic dermatitis, psoriasis and pityriasis amiantacea 6. Other causes for secondary hair casts include infective scalp conditions such as pediculosis capitis, trichorrhexis nodosa, white piedra, and trichomycosis 6. The idiopathic peripillar keratin cast is uncommon. It affects young children and females and not found in association with any disease or scalp condition 8.

Hair casts are commonly seen in females who tightly plate their hair for prolonged periods 9. Hence, they are seen in females who style their hair in braids, twists, dreadlocks, braids, and weave with extensions and in those who use overnight rollers 6. The above-mentioned hairstyles cause excessive traction, leading to local scalp ischemia and inflammation, which is known to promote the development of hair casts 9. Hair casts induced by traction encircle single hair shaft and the parakeratosis is not prominent 9.

Although the condition is benign, if the diagnosis is not established properly, it can cause unnecessary anxiety in both the patient and the treating physician 6.

Pseudonits differential diagnosis includes dandruff, white piedra, trichorrehexis nodosa, monilethrix, trichomycosis and trichonodosis. Pseudonits can be differentiated from nits by an absence of itch (pruritis) and by their mobility along the hair shaft — nits do not slide. Differentiating pseudonits from nits is essential to make the correct diagnosis in order to prevent unnecessary treatment, anxiety, and/or embarrassment. If available, trichoscopic examination will show the tubular shape of pseudonits, which helps differentiate them from head lice (nits), which are oval (Figure 2) 10. In addition to physical removal, keratolytic lotions or shampoos are helpful. França and colleagues 3 have described resolution with a solution of 0.025% retinoic acid, and Ruiz-Villaverde et al 1 have seen good results with a 3% salicylate lotion; both of these agents are keratolytics.

Figure 1. Pseudonits

hair cast pseudonits

Footnote: (A) White structures, mimicking nits, enveloping the hair shafts of a 9-year-old girl. (B) Polarized dermoscopy showing whitish–yellow tubular structures with variable lengths encircling the hair shaft in occipital areas of the patient’s scalp.

[Source 1 ]

Figure 2. Pseudonits trichoscopy

Pseudonits

Footnote: Trichoscopy of hair casts showing elongated tubular structures encircling the hair shaft.

Figure 3. Head lice or pediculosis capitis (nits)

nits

Footnote: Trichoscopy of head lice. Full nits, containing nymph and appearing as ovoid, brown structures with a convex extremity (yellow arrow) are shown. In addition, empty translucent nits, presenting with a plane and fissured free ending (green arrow) can be seen.

[Source 11 ]

Pseudonits causes

The normal outward growth of the hair carries the root sheaths of hair along with it 12. For reasons yet to be determined, there is a failure in the desquamation of some of the root sheaths and they remain encircled to hair shaft after their exit from the hair follicle, which eventually break off and form hair casts 12.

Multiple etiological factors are implicated in their causation. Pseudonits can be caused by several inflammatory scaling conditions such as psoriasis, seborrheic dermatitis, pityriasis amiantacea, dandruff, folliculitis decalvans, pemphigus vulgaris 13, or infective scalp conditions such as pediculosis capitis, trichorrhexis nodosa, white piedra, and trichomycosis 6. Sometimes, hair shaft structural abnormalities such as trichorrhexis nodosa and monilethrix may also cause hair cast pseudonits 14. Residues of cosmetic hair sprays or deodorants and dry shampoos can cause pseudocasts that look very similar to nits 15. Pseudonits hair casts are also seen in traction alopecia as a result of extraction of the root sheaths from excessive tension 2. Apparently, hair cast pseudonits are more frequently seen in females, who tightly plate their hair for prolong period. This excessive traction by causing local scalp ischemia and inflammation promotes the development of pseudonits 16.

In cases of pemphigus vulgaris of scalp, acantholysis occurring in the outer root sheath epithelium can lead to the formation of pseudonits 17.

There are multiple case reports in the literature showing casual association of hair cast pseudonits with lichen planopilaris, pseudopelade of Brocq 18, following psychological trauma 19, propionibacterium acne 20 and familial preponderance 21.

Pseudonits symptoms

Pseudonits may be observed in various dermatological conditions such as psoriasis, seborrheic dermatitis, folliculitis decalvans, and pemphigus vulgaris 13. Pseudonits appearance may vary according to the pathogenesis. Pseudonits can present as whitish scales, frequently seen in seborrheic dermatitis or psoriasis of the scalp, appearing at trichoscopy as easily detachable white, bizarrely shaped, amorphous structures on the hair shaft; although generally easily recognized at clinical examination, in children they can be misdiagnosed as nits 22. The most important characteristic of hair cast pseudonits is its easy sliding along the hair shaft, which helps in differentiating them from other similar conditions.

Pseudonits diagnosis

The diagnosis of pseudonits is generally clinical, but sometimes their presence may cause concern to both patients and physicians. Trichoscopy is a noninvasive and quick-to-perform tool that provides valuable information in a wide range of pediatric and adult hair and scalp conditions 11. It has been reported to be useful for the diagnosis of head and pubic lice, being able to unequivocally identify the presence of parasites and nits, as well as to distinguish full nits from empty nits (Figure 2) 23:279.)).

Pseudonits treatment

The best result is obtained with a solution of 0.025% retinoic acid lotion combined with manual removal of the cylinders with comb, but the condition can recur after stopping medication 24. Ruiz-Villaverde et al 1 have seen good results with a 3% salicylate lotion. Treatment with keratolitic or coaltar shampoos is ineffective. Hair casts tend to recur after discontinuation of the medication 6.

References
  1. Ruiz-Villaverde R, Galán-Gutierrez M. Hair casts (pseudonits). CMAJ. 2013;185(9):E425. doi:10.1503/cmaj.120894 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3680590
  2. Miteva M, Tosti A. Hair and scalp dermatoscopy. J Am Acad Dermatol. 2012 Nov;67(5):1040-8. https://doi.org/10.1016/j.jaad.2012.02.013
  3. França K, Villa RT, Silva IR, et al. Hair casts or pseudonits. Int J Trichology 2011;3:121–2
  4. Sneha M, Savitha A S, Subbarao NT. Unmasking the casts: The true nature of pseudonits. Clin Dermatol Rev [serial online] 2020 https://www.cdriadvlkn.org/text.asp?2020/4/1/65/275238
  5. França K, Villa RT, Silva IR, de Carvalho CA, Bedin V. Hair casts or pseudonits. Int J Trichol 2011;3:121-2.
  6. Lokhande AJ, Lokhande AJ, Sutaria A. Adult onset hair casts: Nits which do not itch! Int J Trichology 2017;9:70-2.
  7. Klingman AM. Hair casts; parakeratotic comedones of the scalp. AMA Arch Derm 1957;75:509-11.
  8. Klingman AM. Hair casts; parakeratotic comedones of the scalp. AMA Arch Derm. 1957;75:509–11.
  9. Tosti A, Miteva M, Torres F, Vincenzi C, Romanelli P. Hair casts are a dermoscopic clue for the diagnosis of traction alopecia. Br J Dermatol 2010;163:1353-5.
  10. Tosti A, Miteva M, Torres F, et al. Hair casts are a dermoscopic clue for the diagnosis of traction alopecia. Br J Dermatol 2010;163:1353–5
  11. Lacarrubba F, Verzì AE, Micali G. Trichoscopy in the Differential Diagnosis of Pseudonits. Skin Appendage Disord. 2019;5(3):142-145. doi:10.1159/000493741 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6489062
  12. Scott MJ Jr., Roenigk HH Jr. Hair casts classification, staining characteristics and differential diagnosis. J Am Acad Dermatol 1983;8:27-32
  13. Casts and pseudocasts. JAAD online Clinical pearl Volume 75, ISSUE 4, e147-e148, October 01, 2016 https://doi.org/10.1016/j.jaad.2016.04.038
  14. Lokhande AJ, Sutaria A. Adult Onset Hair Casts: Nits Which Do Not Itch!. Int J Trichology. 2017;9(2):70-72. doi:10.4103/ijt.ijt_30_17
  15. Ena P, Mazzarello V, Chiarolini F. Hair casts due to a deodorant spray. Australas J Dermatol. 2005 Nov;46(4):274-7. doi: 10.1111/j.1440-0960.2005.00200.x
  16. Tosti A, Miteva M, Torres F, Vincenzi C, Romanelli P. Hair casts are a dermoscopic clue for the diagnosis of traction alopecia. Br J Dermatol. 2010;163:1353–5.
  17. Pirmez R. Acantholytic hair casts: A dermoscopic sign of pemphigus vulgaris of the scalp. Int J Trichology. 2012;4:172–3.
  18. Bayerl C, Moll I. Hair casts in lichen ruber. Hautarzt. 1993;44:37–9.
  19. Held JL, Bernstein RM. Hair casts or pseudonits acquired following psychological trauma. Cutis. 1989;43:380–1.
  20. Wang E, Lee JS, Hee TH. Is Propionibacterium acnes associated with hair casts and alopecia? Int J Trichology. 2012;4:93–7.
  21. Minelli L, Gon AS, Sales NC. Casts: Three cases report and literature review. An Bras Dermatol. 2006;81:159–62.
  22. Vázquez-Herrera NE, Sharma D, Aleid NM, Tosti A. Scalp Itch: A Systematic Review. Skin Appendage Disord. 2018;4(3):187-199. doi:10.1159/000484354
  23. Tang JQ, Ran X, Ran YP. Cover Image: dermoscopy in vivo for the life cycle of Phthirus pubis. Br J Dermatol. 2017 Jan;176((1
  24. Taïeb A, Surlève-Bazeille JE, Maleville J. Hair casts. A clinical and morphologic study. Arch Dermatol 1985;121:1009-13.
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