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Year : 2023  |  Volume : 17  |  Issue : 1  |  Page : 19-27

Psoriasis neurodermiformis, verrucous psoriasis, and psoriasiform keratosis: A clinicopathological evaluation

Department of Dermatology, Katihar Medical College, Karim Bagh, Katihar, Bihar, India

Date of Submission26-Apr-2022
Date of Decision04-Aug-2022
Date of Acceptance04-Aug-2022
Date of Web Publication14-Sep-2022

Correspondence Address:
Dr. Aditya Kumar Bubna
Department of Dermatology, Katihar Medical College, Karim Bagh, Katihar, Bihar
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/tjd.tjd_67_22

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Background: Psoriasis neurodermiformis (PN) and verrucous psoriasis (VP) are two distinct forms of psoriasis characterized by thickened plaques, whose proper description in most dermatologic texts is still lacking. Psoriasiform keratosis (PK) is a recently described clinical entity characterized by a solitary keratotic plaque whose microscopic findings simulate psoriasis. Aim: To compare and evaluate the clinical and histological profile of PN, VP and PK, and systematically characterize each of them. Settings and Design: This was a prospective, descriptive study done on a total of 51 patients, who were diagnosed with PN, VP and PK based on certain clinical criteria. The study was done at a teaching hospital in eastern India. Methods and Materials: The study was carried out on a total of 51 patients presenting with thickened psoriasiform plaques, who visited our outpatient department, over a period of 9 months. They were then carefully evaluated clinically (along with their demographic profile), followed by meticulous microscopic assessment. Each biopsy specimen was then categorically evaluated to enable a precise diagnostic conclusion. Statistical Analysis: As all values in our study were qualitative, they were expressed as numeric values and percentages. Results: Out of 51 patients, 18 were diagnosed as PN, 19 with VP and 14 with PK. PN demonstrated an equal gender distribution, whereas in VP and PK a male preponderance was apparent. History of past/present psoriasis was positive in only one patient diagnosed with VP. Intensity of pruritus was marked in 88.88%, 21.05% and 14.28% of patients with PN, VP and PK respectively. Dorsa of feet was the commonest site of involvement in PN and VP. In PK, the shin was the predominating site. VP presented clinically as mammillated, verrucous and crateriform phenotypes. PN and PK however, demonstrated single clinical patterns. Microscopically, none of the specimens satisfied all the 7 epidermal criteria set forth by Ackerman. In each slide Trozak’s histologic psoriasiform numeric score was >10. Conclusion: PN, VP and PK are certainly not as rare as previously considered. Mammillated VP closely mimics PN clinically. Crateriform VP is an extremely rare phenotypic expression encountered. Histological findings of papillomatosis, buttressing and anastomosing rete ridges and a dense dermal lymphocytic infiltrate point more in favor toward VP. Detecting solitary keratotic plaques with a psoriasiform histology should allow clinicians to consider the possibility of PK.

Keywords: Histopathology, psoriasiform keratosis, psoriasis neurodermiformis, verrucous psoriasis

How to cite this article:
Patil NK, Bubna AK. Psoriasis neurodermiformis, verrucous psoriasis, and psoriasiform keratosis: A clinicopathological evaluation. Turk J Dermatol 2023;17:19-27

How to cite this URL:
Patil NK, Bubna AK. Psoriasis neurodermiformis, verrucous psoriasis, and psoriasiform keratosis: A clinicopathological evaluation. Turk J Dermatol [serial online] 2023 [cited 2023 Mar 25];17:19-27. Available from: https://www.tjdonline.org/text.asp?2023/17/1/0/356052

  Introduction Top

Psoriasis is a commonly encountered papulosquamous disorder in all dermatology clinics, throughout the world.

Although chronic plaque psoriasis is the classical phenotype witnessed; there are a number of other clinical presentations of the disease, which the clinician ought to be aware about.

Amongst them, patterns comprising thickened plaques have been specifically identified and studied both clinically and microscopically.

Included within this spectrum, are two variants of psoriasis; namely psoriasis neurodermiformis (PN) and verrucous psoriasis (VP) that have been elaborated in the recent past.[1],[2] Of late, another condition referred to as psoriasiform keratosis (PK) has been elucidated, which again manifests as a thickened psoriatic plaque.[3] The etiology of PK still remains elusive, and whether it represents a unifocal presentation of psoriasis needs closer evaluation.

Our study was an attempt to analyze PN, VP and PK and determine subtle differences in their clinical and histologic morphologies; thereby allowing a precise conclusion while confronting these entities.

  Methods and Materials Top

This was a prospective, descriptive study conducted over a period of 9 months in the department of dermatology of our institute, after obtaining permission by the institutional ethical clearance committee (Registration number: KMC/IEC/Dept.Res./013/2021-2024DVL).

Only freshly diagnosed patients or patients without any form of treatment for the past 6 months were included in the study.

We were able to get a total of 51 patients during this time frame, of which 18 demonstrated clinical findings of PN, 19 delineated phenotypic features of VP and the remaining 14 expressed characteristics suggestive of PK.

Once patients were enrolled, a written and informed consent was obtained from each of them, following which relevant history concerning the disease was recorded and a complete clinical examination done, which was furthered by a cutaneous biopsy, that was sent for histopathological examination.

Based on certain clinical criteria (that were proposed by the authors of the current study), each patient was designated to one of the three diagnostic entities as stated above; details of which have been elaborated in [Table 1]. In order to fit a designated entity, fulfillment of each of the aforementioned criterion (as detailed in [Table 1]), in the respective group was mandatory, the exception being freshly diagnosed cases, wherein the criterion taking into account the responsiveness to topical/intralesional steroids was not required. [Table 2] details the number of freshly and previously diagnosed cases (following topical/intralesional steroid therapy and their responsiveness to treatment) of our study subjects.{Table 1} {Table 2}

Biopsy findings were primarily delineated as psoriasiform, based on 7 epidermal criteria originally put forth by Ackerman et al,[4] and include neutrophilic microabscesses in the stratum corneum, confluent parakeratosis, hypogranulosis, neutrophilic microabscesses in the spinous layer, slight spongiosis, thinning of suprapapillary plates and regular acanthosis.

This was succeeded by assigning a numeric histologic score as per the grading system designed by Trozak.[5] All slides were then categorically evaluated to determine explicit histological differences in the dermal and epidermal mileu for each of these 3 entities, to enable a precise diagnostic conclusion.

Statistical analysis

As all data in our study were categorical, they were expressed as numeric values and percentages.

  Results Top

Out of the 51 patients studied 18 were clinically diagnosed with PN, 19 with VP and 14 with PK. The salient clinical and demographic profile of each has been outlined in [Table 2].

Histologically, we assessed each slide with regard to epidermal and dermal parameters, to identify the existence of major as well as subtle differences in each of the conditions described. These findings have been annotated in [Table 3].{Table 3}

  Discussion Top

Our main purpose in conducting this study was an endeavour to delineate the above variants of psoriasis, as their proper description in most dermatologic texts is lacking.

PN, also referred to as lichenified psoriasis, is a variant of psoriasis characterized by accentuated skin surface markings [Figure 1]a.[6] It may not be as rare as accounted. More often than not, it could get misdiagnosed as lichen simplex chronicus (LSC) owing to their close clinical approximation. However, there do exist subtle differences between both clinically; meticulous scrutiny of which could be of considerable help [Table 4].{Figure 1} {Table 4}

Nevertheless, in many cases, this may prove quite challenging, owing to overlapping features that manifest.

Further, absence of Auspitz sign (though not diagnostic, yet a valuable tool) in PN could prevent prompt recognition of the condition. Histopathology therefore becomes mandatory for a precise conclusion.

Despite the presence of overlapping findings in both conditions microscopically, specific features pertaining to both disorders can enable the dermatopathologist in arriving at an end result [Table 4].

Regardless of histological features stated, it has been witnessed that even untreated clinically active psoriatic lesions lack a completely characteristic microscopic architecture.[7] Besides, variable histological findings have been observed even within a single psoriatic plaque, thereby implying that all features of psoriasis may not be viewed very often from just a single specimen.[8] Histological diagnosis therefore relies on an aggregate of attributes; some of which are seen distinctively in psoriasis and others more common to other dermatoses.

Likewise, in our study, none of the participants fulfilled all 7 epidermal features as stated above. However, each of these criteria was expounded in significant frequencies amongst our cohorts when carefully taken one by one.

Based on Trozak’s histological grading system we scored each slide to obtain a numeric degree of psoriasiform changes.[5]

All our patients with PN demonstrated a numeric psoriasiform grade between 11 and 15 (out of a maximum score of 19), which we consider fitting in making a final diagnosis of psoriasis. Although the apt cut off value has not been determined by Trozak, we regard scores >10 acceptable in making a confirmatory histological diagnosis of psoriasis.

Previous publications regarding the application of Trozak’s grading for histopathological evaluation of psoriasis is scant. Literature search revealed only one recent study from India done on classical psoriatic plaques wherein a mean score of 9.44 (in 50 patients) was considered sufficient to label the histological specimen as psoriasis.[9] The reduced utility of Trozak’s histologic scoring by most clinicians could be attributed to the fact that in most cases the focus by dermatologists is primarily on clinical assessment scores like the PASI (Psoriasis Area and Severity Index) score, rather than microscopic scoring.

Further the role of histopathology becomes more relevant in atypical phenotypes of psoriasis where clinical diagnosis is not straightforward, thereby warranting scrupulous microscopic assessment in order to obtain a concrete conclusion. In such scenarios, Trozak’s grading system could be of substantial value.

As our study dealt with three atypical presentations of psoriasis, histological grading helped us greatly in evaluating our cohorts. It was only after careful study did we conclude in favor of a score >10 to confer a confirmatory diagnosis of psoriasis microscopically.

Vertically oriented dermal collagen bundles were identified in 10 of our diagnosed patients with PN. Unlike LSC, these bundles were not thickened. This arrangement of collagen bundles has been linked to increased scratching owing to the release of various chemical mediators secondary to activation of the neuro-cutaneous axis involved in psoriasis. Its occurrence therefore should not be an argument to refute a diagnosis of psoriasis.

The mammillated variant of VP can closely mimic PN clinically. VP is a rare variant of psoriasis that requires detailed elucidation. To compound things further, this form of psoriasis presents in four morphological patterns.[2] These include dome shaped papules/plaques, crateriform papules/nodules, annular/oval verrucous plaques and the mammillated phenotype. If the clinician is not acquainted regarding these presentations, there could be a high likelihood of diagnostic discrepancy.

Within our cohorts, 8 (42.11%) presented with the mammillated variant [Figure 1b], 10 (52.63%) were consistent with the verrucous morphology [Figure 1c] and 1(5.26%) displayed features suggestive of crateriform VP [Figure 1d]. In the report by Khalil and colleagues,[2] mammillated VP was the most common presenting morphology and was observed in 67% of their cohorts. The remaining 33% manifested VP in the form of agminated, tan white papules.

Linear verrucous plaques were the characteristic finding in a report from Chennai,[10] and numerous verrucous plaques as the sole morphology of VP was demonstrated in the publication by Wakamatsu et al.[11]

Erkek and Bozdogan[12] documented a rare expression of VP in the form of an annular outline of verrucous psoriatic plaques and Garvie et al.,[13] reported a phenotype of VP that closely simulated verrucous carcinoma in an 81 year old male.

Crateriform lesions was another rare presentation of VP that was reported by Nakamura et al.,[14] in 1994. Following this, to the best of our knowledge no such report of crateriform VP has been published.

Our patient who presented with crateriform VP also displayed lesions of chronic plaque psoriasis. Initially a diagnosis of keratoacanthoma (KA) was contemplated for this lesion, but histology eventually ruled that out.

It would be worthwhile to note that KA has been reported in patients of psoriasis.

In 1961, Vickers and Ghadially reported the first case characterized by multiple KAs emerging over psoriatic plaques treated with coal tar.[15]

A year later, Clendenning et al.,[16] in their paper elaborated the occurrence of KAs in a patient of generalized pustular psoriasis.

Almost two decades later, KAs originating at psoriatic treatment sites was again elucidated in two papers; one from India and the other from Canada.[17],[18]

Recently, Rehlan and colleagues reported the formation of multiple KAs over healing psoriatic plaques.[19]

Plausible explanations regarding the development of KAs in psoriasis, include tar therapy, immunosuppressive effects of methotrexate, chronic inflammation, phototherapy and epithelial injury as a consequence of psoriasis per se.

Interestingly, in all these reports KA developed over a time period that ranged from 4 months to 43 years after the initial presentation of psoriasis, thereby representing a secondary phenomenon.

In our patient, on the other hand crateriform VP and chronic plaque psoriasis presented concurrently.

Further, as crateriform VP is extremely rare, there could be a high likelihood for clinicians to preclude its inclusion in the list of differentials for crateriform lesions. It therefore would be prudent for all dermatologists in being cognizant with this presentation of VP.

Apart from the regular histological findings of psoriasis, epidermal invagination and neutrophilic exocytosis were additional features reported by Nakamura et al.,[14] for crateriform VP. In our patient however, neutrophilic exocytosis was not clearly evident. Hyperkeratosis, confluent parakeratosis, scattered neutrophils in the horny layer, a cup shaped epidermal invagination, suprapapillary thinning and elongated rete ridges with buttressing and anastomoses were the predominant findings identified on microscopy [Figure 2]a and b.{Figure 2}

VP was confined to the lower limbs in all our participants with dorsa of feet (89.94%) being the most common site. In contrast, the study from Tampa, Florida, demonstrated the knees to be the most common site (50%), followed by the elbows (33%) and hands (17%).[2] In the report from Turkey, posterior truncal location of lesions were documented.[12] On the other hand, findings of Rajendran et al.,[10] and Wakamatsu et al.,[11] closely aligned with our observation of lower limb involvement.

Acanthosis, papillomatosis, buttressing of rete ridges, Munro’s microabcessess and spongiform pustules of kogoj were seen in 100%, 78.94%, 100%, 52.63% and 47.36% of our VP study subjects respectively. In the study by Khalil et al.,[2] similarly acanthosis and buttressing of rete ridges were observed in all their cohorts, whereas munro’s microabcessess and spongiform pustules of kogoj were seen in 50% and 92% of their patients respectively.

Further, we observed that spongiform pustules and neutrophills within the stratum corneum in VP were more pronounced than those observed in PN [Figure 3]a and b. Papillomatosis was another significant observation on microscopy in VP [Figure 3]c. Also, unlike the regular camel foot elongation observed in PN, rete ridges in VP demonstrated buttressing and anastomoses as a hallmark finding.{Figure 3}

A numeric psoriasiform grade between 11 and 16 was documented in all 19 patients diagnosed with VP.

Diabetes mellitus (DM) has been proposed as a predisposing factor for VP, secondary to the occurrence of microangiopathy and macroangiopathy.[2] Increased susceptibility to the development of VP has also been documented in patients with pulmonary dysfunction and phlebitis, in relation to tissue anoxia.[2] Further, Scavo et al.,[20] have reported VP in a patient with chronic hepatitis C treated with interferon. These postulations however need further validation.

Owing to rare reports of VP, a clear pathogenesis remains obscure. It has been propounded that a secondary epithelial response to repeated trauma in patients with preexisting psoriasis or psoriatic diathesis could be the pathogenic mechanism involved.[2]

For PN, constant rubbing over pruritic psoriatic plaques and the development of psoriasis as a consequence of koebnerization secondary to constant friction in patients with LSC are suggested interpretations for its pathogenesis.[1]

PK is a clinical entity that was first illustrated in 2007 by Walsh and colleagues.[3] It is characterized by solitary, unifocal, sharply demarcated keratotic plaques, that demonstrate psoriasiform changes on microscopy [Figure 4]a, b, c and d. Since its initial description, there have been a few more reports reiterating this observation.[21],[22],[23] However though, data with regard to PK still remains scant.{Figure 4}

The exact etiology of PK remains elusive and has been suggested to be a unique form of epithelial proliferation, culminating in microscopic psoriasiform changes. Further, its inclusion to the list of cutaneous acanthomas has been recommended recently.[21]

Out of our 14 patients, 13 presented with a singular lesion, with one patient having two closely situated keratotic plaques involving the right knee. Majority of our patients were in the 3rd decade, which was in sharp contrast to the observation by Walsh et al.,[3] and Mutasim,[21] in which patients belonging to the 7th and 8th decade predominated.

The lower limb was the only site involved in all our participants. This differed from the findings observed by Walsh et al.,[3] wherein only 39% of their cohorts demonstrated involvement of the lower limb. In the remaining 61%, sites included the scalp, forehead, neck, shoulder, upper extremities and back. However, with respect to lesional location, findings of Mutasim,[21] Carbone[22] and Pires[23] were in consonance with our findings, allowing us to consider the lower extremity as the commonest site regarding the occurrence of PK. Analogous to previous reports, we also considered Bowen’s disease, clear cell acanthoma, VP, lichenoid keratosis and psoriasiform eczema as major differentials. In one patient however, owing to a slightly more pronounced thickened texture, possibilities of deep mycosis and tuberculosis cutis were also contemplated, which eventually were ruled out by microscopic examination along with Periodic Acid Schiff staining.

Histologically, parakeratosis was identified in 5 of our 14 patients. This differed from the findings of Mutasim[21] and Walsh et al.,[3] wherein parakeratosis was delineated in all their participants. Hypogranulosis was observed in only 28.57% of our patients, in contrast to 69.2% of the subjects in the study from Cincinnati.[21]

Similar to our findings, acanthosis was identified in all histological specimens by Mutasim.[21] Suprapapillary thinning was seen in 78.57% of our participants. This was in contrast to the observation by Mutasim[21] in which none of the slides demonstrated suprapapillary thinning.

The dermal infiltrate in all our patients was composed primarily of lymphocytes. In most of our patients (72.42%), the distribution of inflammatory cells was mild to moderate. This was in consonance with the findings of Walsh et al.,[3] and Mutasim.[21]

The numeric histological psoriasiform score ranged from 11 to 13 amongst our PK study subjects.

On comparing PK, with PN and VP, no confusion arose in contrasting it from them clinically.

Histologic overlap though, did occur. Distinguishing VP from PK histologically was not difficult. Certain distinctive findings like anastomosing and buttressing of rete ridges, papillomatosis, denser dermal inflammatory infiltrate and a more pronounced expression of munro’s microabscesses/spongiform pustules of kogoj were more specific for VP and enabled the authors to obtain a concrete histological conclusion.

However, there was considerable overlap between PN and PK microscopically; thereby making clinical correlation essential to arrive at a final/specific diagnosis in these cases.

  Conclusion Top

Although the concept of PN, VP and PK may not be very novel, yet we felt the need to revisit these entities owing to their close similarity with a number of other dermatoses.

Further, because of paucity regarding their representation in medical literature, and their non resemblance to classical psoriatic plaques; often there could be a high likelihood of an incorrect diagnosis.

Moreover, different phenotypes of VP; and the pattern of rete ridges observed under microscopy could further pose a diagnostic challenge to the dermatologist/pathologist if they are not well versed with these findings.

It therefore becomes imperative to adopt a systematic clinicopathological evaluation to arrive at a concrete conclusion.

Besides, we also need to be aware about the fact that it is very unlikely to detect each and every finding of psoriasis in an individual biopsy specimen. Scoring each slide numerically according to Trozak’s grading could therefore be of practical significance.

According to our observation, we are of the opinion that any score >10 is acceptable to finalize a histological diagnosis of psoriasis.

Lastly, based on our findings we do not consider PN, VP and PK to be rare entities. This rarity could be attributed to their lower reporting.


Dr Leena Dennis Joseph; MBBS, MD (Professor, Department of Pathology, Sri Ramachandra University, Porur, Chennai 600116) for helping us with histopathologic evaluation.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

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Khalil FK, Keehn CA, Saeed S, Morgan MB. Verrucous psoriasis: A distinctive clinicopathologic variant of psoriasis. Am J Dermatopathol 2005;27:204-7.  Back to cited text no. 2
Walsh SN, Hurt MA, Santa Cruz DJ. Psoriasiform keratosis. Am J Dermatopathol 2007;29:137-40.  Back to cited text no. 3
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Scavo S, Gurrera A, Mazzaglia C, Magro G, Pulvirenti D, Gozzo E, et al. Verrucous psoriasis in a patient with chronic C hepatitis treated with interferon. Clin Drug Investig 2004;24:427-9.  Back to cited text no. 20
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