Follicular Psoriasis

This case evaluates follicular psoriasis, an uncommon variant manifesting as scaly folliculocentric 
hyperkeratotic eruptions of the trunk and extremities. 

Psoriasis is a common autoimmune dermatosis representing an interplay between certain genetic predisposing factors along with clonally restricted T_h1 T cells responding to epidermal keratinocyte derived antigen. A unique IL-17/IL-23 cytokine rich milieu is pathogenetically significant and conducive to its salient histomorphologic features, such as epideram hyperplasia and intraepidermal influx of neutrophils. Many of the effector intraepidermal lymphocytes are of the CD8 subset; myeloid dendritic cells are also key players in the evolution of psoriasis.¹

The worldwide prevalence of psoriasis depends on age and geographic location. In the United States, the incidence of psoriasis is approximately 2%, with a higher frequency in the Caucasian population.² The classic cutaneous manifestation is that of plaque psoriasis also referred to as psoriasis vulgaris. Characteristic lesions are described as elevated well-circumscribed erythematous plaques covered by silvery scales that exhibit the Auspitz sign upon removal.

Follicular psoriasis (FP) is an uncommon variant manifesting as a scaly folliculocentric hyperkeratotic eruptions of the trunk and extremities, irrespective of the presence or absence of conventional lesions of psoriasis vulgaris. 

The incidence of FP is unknown with roughly 23 reported cases emphasizing its rarity given the overall incidence of conventional psoriasis in the general population. Due to the lack of awareness, the clinical presentation is often misdiagnosed as other follicular dermatoses, including bacterial folliculitis, pityriasis rubra pilaris, keratosis pilaris, or follicular eczema.

Case Presentation

A 61-year-old white woman presented with a sudden and self-remitting pruritic papular rash of the bilateral forearms and bilateral lower legs of several months’ duration. She denied any constitutional symptoms. The patient had no known history of kidney, liver, thyroid, or hematologic diseases. Other family members did not have a similar eruption. 

Physical examination revealed numerous erythematous crusted papules that extended to the superior and inferior back (Figures 1A-D). Symptomatic palliation was seen with the use of a pimecrolimus cream (Elidel). 

Multiple shave biopsies were performed on the right superior back, right inferior back, right upper arm, and right forearm. Light microscopic examination revealed an extensive pustular folliculocentric process. There was permeation of the outer root sheath epithelium by neutrophils. In addition, the ostium of the follicle was occluded by keratin intimately admixed with neutrophils (Figures 2A and B). 

The background epidermis exhibited classic features of a psoriasiform diathesis, the hallmarks being those of neutrophil-imbued parakeratosis, granular cell layer loss and dilated dermal papillae capillaries lying in intimate apposition to the basal layer of the epidermis (Figures 2C and D). Direct immunofluorescence revealed entrapment of immunoglobulin and complement within the stratum corneum along with variable granular deposition of complement along the dermal epidermal junction.  

A diagnosis of FP was made. The patient was placed on a tumor necrosis factor inhibitor that resulted in regression of the eruption. It was subsequently established that the patient had a remote history of psoriasis.  

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Discussion

This patient presented with diagnostic features of FP in the setting of an antecedent history of psoriasis vulgaris. As expected our patient demonstrated an excellent response to biologic therapy. Our case appears to be prototypic for this rare variant of psoriasis based on our review of the literature. 

The first paper referencing FP was published by Michelson in 1958 as the unusual psoriasis.³ The reported cases describing this follicular presentation of psoriasis were in children. 

However, Stankler and Ewen published the first paper recognizing FP as a distinct entity in 1981.⁴ The authors subdivided FP into 2 broad categories: the adult type and juvenile type.³ The adult group was characterized by a total of 6 patients, 5 women and 1 man ranging in age from 18 to 69 years. All patients had a prior diagnosis of psoriasis. This group presented with bilateral follicular lesions on the thighs in a background of more conventional lesions of psoriasis vulgaris. The juvenile group comprised a total of 4 patients, 1 girl and 3 boys younger than 10 years. A prior diagnosis of psoriasis under the age of 10 was rendered in all 4 patients. This group presented with asymmetric plaque-like follicular lesions on the trunk and axilla. 

In the series of FP by Ploysangam and Mutasim, a total of 5 patients, 4 women and 1 man, ranging in age from 23 to 73 years had clinical symptoms of erythematous hyperkeratotic follicular papules on the trunk and extremities.⁵ Only 2 patients had a prior history of psoriasis, both exhibiting a peculiar localization of psoriasis to the scalp. There appeared to be an association with diabetes mellitus and being of African ancestry. 

Several additional anecdotal case reports describe FP. Arps and colleagues described a 46-year-old diabetic black woman with symptomatic pruritus with folliculocentric hyperkeratotic papules on the scalp, neck, back, and extremities.⁶ This patient had no previous diagnosis of psoriasis and lacked the classical findings for psoriasis vulgaris. Thomas and colleagues presented a case of FP in an 18-year-old Asian man who exhibited bilateral follicular lesions involving the thighs, calves, and arms. This patient was initially diagnosed with lichen planopilaris.⁷ Patil and colleagues described a 13-year-old boy who had symptomatic scaling and erythema of the skin that began as horny papules on the knees and elbows.⁸ These lesions evolved into erythematous scaly papules encompassing the entire body. 

The clinical presentations and microscopic examinations in all of the previously described reports were similar to the findings in our case. A summary of these cases, including our patient, is presented the Table. 

The basis for the folliculocentricity of this variant of psoriasis is unclear. Secondary progressive involvement of the integument in patients with an established history of conventional psoriasis seems plausible given the documented history of preexisting psoriasis in most patients and the well-known predilection of psoriasis for those areas of the skin devoid of follicles most notably the palms, soles, and nails. Perhaps a further explanation lies in inherent tropism of common viruses such as varicella, measles, polyomavirus, human herpesvirus 6, and human herpesvirus 7 for the hair follicle. The innate immune response involves the recruitment of plasmacytoid and myeloid dendritic cells into the infected follicles, a source of type I interferon which enhances both the adaptive and innate limbs of immunity. Hence, the follicle could have a microenvironment conducive to the development of the psoriatic lesion given the known role of myeloid dendritic cells, type I interferons, and T cells in the pathogenesis of the earlier phases of psoriatic inflammation.^9-11

Dr Magro is the director of dermatopathogy at Well Cornell Medicine in New York, NY. For more information, please visit www.weillcornelldermpath.com.

Disclosure: The author reports no relevant financial relationships.  

References

1. Grine L, Dejager L, Libert C, Vandenbroucke R. An inflammatory triangle in psoriasis: TNF, type I IFNs and IL-17. Cytokine Growth Factor Rev. 2015;26(1):25-33. 

2. Langley RG, Krueger GG, Griffiths CE. Psoriasis: epidemiology, clinical features, and quality of life. Ann Rheum Dis. 2005;64(suppl 2):ii18-23; discussion ii24-25.

3. Michelson HE. The unusual in psoriasis. AMA Arch Derm. 1958;78(1):9-13.

4. Stankler L, Ewen SW. Follicular psoriasis. Br J Dermatol. 1981;104(2):153-156.

5. Ploysangam T, Mutasim DF. Follicular psoriasis: an under-reported entity. A report of five cases. Br J Dermatol. 1997;137(6):988-991.

6. Arps DP, Chow C, Lowe L, Chan MP. Follicular psoriasis. J Cutan Pathol. 2013;40(10):859-862. 

7. Thomas LJ, Dadzie OE, Francis N, Morar N. Follicular psoriasis–A forgotten entity? Open Dermatol J. 2010;4:95-96.

8. Patil JD, Chaudhary SS, Rani N, Mishra AK. Follicular psoriasis causing erythroderma in a child: A rare presentation. Indian Dermatol Online J. 2014;5(1):63-65. 

9. Nguyen CV, Farah RS, Maguiness SM, Miller DD. Follicular psoriasis: Differentiation from pityriasis rubra pilaris-an illustrative case and review of the literature. Pediatr Dermatol. 2017;34(1):e65-e68.

10. Babino G, Moscarella E, Longo C, et al. Follicular psoriasis: an under-recognized condition. J Eur Acad Dermatol Venereol. 2016;30(8):1397-1399. 

11. Javor S, Drago F, Parodi A. Understanding a role of folliculotropic viral infections in the pathogenesis of psoriasis. Med Hypotheses. 2016;89:101. 

This case evaluates follicular psoriasis, an uncommon variant manifesting as scaly folliculocentric 
hyperkeratotic eruptions of the trunk and extremities. 

Psoriasis is a common autoimmune dermatosis representing an interplay between certain genetic predisposing factors along with clonally restricted T_h1 T cells responding to epidermal keratinocyte derived antigen. A unique IL-17/IL-23 cytokine rich milieu is pathogenetically significant and conducive to its salient histomorphologic features, such as epideram hyperplasia and intraepidermal influx of neutrophils. Many of the effector intraepidermal lymphocytes are of the CD8 subset; myeloid dendritic cells are also key players in the evolution of psoriasis.¹

The worldwide prevalence of psoriasis depends on age and geographic location. In the United States, the incidence of psoriasis is approximately 2%, with a higher frequency in the Caucasian population.² The classic cutaneous manifestation is that of plaque psoriasis also referred to as psoriasis vulgaris. Characteristic lesions are described as elevated well-circumscribed erythematous plaques covered by silvery scales that exhibit the Auspitz sign upon removal.

Follicular psoriasis (FP) is an uncommon variant manifesting as a scaly folliculocentric hyperkeratotic eruptions of the trunk and extremities, irrespective of the presence or absence of conventional lesions of psoriasis vulgaris. 

The incidence of FP is unknown with roughly 23 reported cases emphasizing its rarity given the overall incidence of conventional psoriasis in the general population. Due to the lack of awareness, the clinical presentation is often misdiagnosed as other follicular dermatoses, including bacterial folliculitis, pityriasis rubra pilaris, keratosis pilaris, or follicular eczema.

Case Presentation

A 61-year-old white woman presented with a sudden and self-remitting pruritic papular rash of the bilateral forearms and bilateral lower legs of several months’ duration. She denied any constitutional symptoms. The patient had no known history of kidney, liver, thyroid, or hematologic diseases. Other family members did not have a similar eruption. 

Physical examination revealed numerous erythematous crusted papules that extended to the superior and inferior back (Figures 1A-D). Symptomatic palliation was seen with the use of a pimecrolimus cream (Elidel). 

Multiple shave biopsies were performed on the right superior back, right inferior back, right upper arm, and right forearm. Light microscopic examination revealed an extensive pustular folliculocentric process. There was permeation of the outer root sheath epithelium by neutrophils. In addition, the ostium of the follicle was occluded by keratin intimately admixed with neutrophils (Figures 2A and B). 

The background epidermis exhibited classic features of a psoriasiform diathesis, the hallmarks being those of neutrophil-imbued parakeratosis, granular cell layer loss and dilated dermal papillae capillaries lying in intimate apposition to the basal layer of the epidermis (Figures 2C and D). Direct immunofluorescence revealed entrapment of immunoglobulin and complement within the stratum corneum along with variable granular deposition of complement along the dermal epidermal junction.  

A diagnosis of FP was made. The patient was placed on a tumor necrosis factor inhibitor that resulted in regression of the eruption. It was subsequently established that the patient had a remote history of psoriasis.  

Article continues on page 2

{{pagebreak}}

Discussion

This patient presented with diagnostic features of FP in the setting of an antecedent history of psoriasis vulgaris. As expected our patient demonstrated an excellent response to biologic therapy. Our case appears to be prototypic for this rare variant of psoriasis based on our review of the literature. 

The first paper referencing FP was published by Michelson in 1958 as the unusual psoriasis.³ The reported cases describing this follicular presentation of psoriasis were in children. 

However, Stankler and Ewen published the first paper recognizing FP as a distinct entity in 1981.⁴ The authors subdivided FP into 2 broad categories: the adult type and juvenile type.³ The adult group was characterized by a total of 6 patients, 5 women and 1 man ranging in age from 18 to 69 years. All patients had a prior diagnosis of psoriasis. This group presented with bilateral follicular lesions on the thighs in a background of more conventional lesions of psoriasis vulgaris. The juvenile group comprised a total of 4 patients, 1 girl and 3 boys younger than 10 years. A prior diagnosis of psoriasis under the age of 10 was rendered in all 4 patients. This group presented with asymmetric plaque-like follicular lesions on the trunk and axilla. 

In the series of FP by Ploysangam and Mutasim, a total of 5 patients, 4 women and 1 man, ranging in age from 23 to 73 years had clinical symptoms of erythematous hyperkeratotic follicular papules on the trunk and extremities.⁵ Only 2 patients had a prior history of psoriasis, both exhibiting a peculiar localization of psoriasis to the scalp. There appeared to be an association with diabetes mellitus and being of African ancestry. 

Several additional anecdotal case reports describe FP. Arps and colleagues described a 46-year-old diabetic black woman with symptomatic pruritus with folliculocentric hyperkeratotic papules on the scalp, neck, back, and extremities.⁶ This patient had no previous diagnosis of psoriasis and lacked the classical findings for psoriasis vulgaris. Thomas and colleagues presented a case of FP in an 18-year-old Asian man who exhibited bilateral follicular lesions involving the thighs, calves, and arms. This patient was initially diagnosed with lichen planopilaris.⁷ Patil and colleagues described a 13-year-old boy who had symptomatic scaling and erythema of the skin that began as horny papules on the knees and elbows.⁸ These lesions evolved into erythematous scaly papules encompassing the entire body. 

The clinical presentations and microscopic examinations in all of the previously described reports were similar to the findings in our case. A summary of these cases, including our patient, is presented the Table. 

The basis for the folliculocentricity of this variant of psoriasis is unclear. Secondary progressive involvement of the integument in patients with an established history of conventional psoriasis seems plausible given the documented history of preexisting psoriasis in most patients and the well-known predilection of psoriasis for those areas of the skin devoid of follicles most notably the palms, soles, and nails. Perhaps a further explanation lies in inherent tropism of common viruses such as varicella, measles, polyomavirus, human herpesvirus 6, and human herpesvirus 7 for the hair follicle. The innate immune response involves the recruitment of plasmacytoid and myeloid dendritic cells into the infected follicles, a source of type I interferon which enhances both the adaptive and innate limbs of immunity. Hence, the follicle could have a microenvironment conducive to the development of the psoriatic lesion given the known role of myeloid dendritic cells, type I interferons, and T cells in the pathogenesis of the earlier phases of psoriatic inflammation.^9-11

Dr Magro is the director of dermatopathogy at Well Cornell Medicine in New York, NY. For more information, please visit www.weillcornelldermpath.com.

Disclosure: The author reports no relevant financial relationships.  

References

1. Grine L, Dejager L, Libert C, Vandenbroucke R. An inflammatory triangle in psoriasis: TNF, type I IFNs and IL-17. Cytokine Growth Factor Rev. 2015;26(1):25-33. 

2. Langley RG, Krueger GG, Griffiths CE. Psoriasis: epidemiology, clinical features, and quality of life. Ann Rheum Dis. 2005;64(suppl 2):ii18-23; discussion ii24-25.

3. Michelson HE. The unusual in psoriasis. AMA Arch Derm. 1958;78(1):9-13.

4. Stankler L, Ewen SW. Follicular psoriasis. Br J Dermatol. 1981;104(2):153-156.

5. Ploysangam T, Mutasim DF. Follicular psoriasis: an under-reported entity. A report of five cases. Br J Dermatol. 1997;137(6):988-991.

6. Arps DP, Chow C, Lowe L, Chan MP. Follicular psoriasis. J Cutan Pathol. 2013;40(10):859-862. 

7. Thomas LJ, Dadzie OE, Francis N, Morar N. Follicular psoriasis–A forgotten entity? Open Dermatol J. 2010;4:95-96.

8. Patil JD, Chaudhary SS, Rani N, Mishra AK. Follicular psoriasis causing erythroderma in a child: A rare presentation. Indian Dermatol Online J. 2014;5(1):63-65. 

9. Nguyen CV, Farah RS, Maguiness SM, Miller DD. Follicular psoriasis: Differentiation from pityriasis rubra pilaris-an illustrative case and review of the literature. Pediatr Dermatol. 2017;34(1):e65-e68.

10. Babino G, Moscarella E, Longo C, et al. Follicular psoriasis: an under-recognized condition. J Eur Acad Dermatol Venereol. 2016;30(8):1397-1399. 

11. Javor S, Drago F, Parodi A. Understanding a role of folliculotropic viral infections in the pathogenesis of psoriasis. Med Hypotheses. 2016;89:101.