Unilateral Psoriasis on the Left Leg and Poliomyelitis of the Right Leg: A Case Report and Review of the Etiology

Psoriasis is a multifactorial immunological chronic skin disease that is not uncommon and the reported prevalence is approximately 2%. However, unilateral psoriasis is very rare, especially when the disease is confined to the leg on one side. We report a 59-year-old male with a polio-affected right leg who presented with psoriatic papules on the left leg, which was ultimately diagnosed as unilateral psoriasis and successfully treated with topical steroid and vitamin D agents. Furthermore, we review the etiology of unilateral psoriasis and propose that the Koebner phenomenon has acted as the triggering and aggravating factor of unilateral psoriasis in this patient.

A 59-year-old Korean male with right-leg poliomyelitis visited the dermatology clinic in December 2019. Three months before, he had erythematous exfoliative skin lesions on the left leg. The patient recalled that there were papules and plaques with scales affecting his entire body 31 years ago and that the lesions spontaneously resolved 5 years ago. Three months before visiting our clinic, multiple papules appeared on his left leg. He managed the lesions by applying occlusive dressings with topical agents and wraps three times until the visit to the clinic. Afterward, erythematous exfoliative skin lesions with exudate, odor, and pain appeared in the affected area (Fig. 1). There were no systemic symptoms such as fever. The patient was treated under the diagnosis of irritant contact dermatitis and secondary bacterial infection. The erythematous exfoliative lesions improved, However, papulosquamous lesions confined to the left leg were noted, and a biopsy was performed at the site (Fig. 2).

Fig. 1
(A) Diffuse erythematous exfoliative skin on the anterior side of the left leg at the first visit. (B) The medial side of the left leg. (C) The lateral side of the left leg.

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Fig. 2
(A) Erythematous scaly papules and plaques on the anterior side of the left leg at the 3-month follow-up. (B) The posterior side of the left leg. (C) Left knee.

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The biopsy showed a thickened stratum corneum, dyskeratosis in the epidermis, neutrophil clustering in part of the stratum corneum, regular elongation of the rete ridges and enlarged blood vessels, as well as inflammation in the papillary dermis (Fig. 3). A diagnosis of psoriasis was made based on clinical features and characteristic histopathological findings. Treatment with a combined steroid and vitamin D topical agent was initiated, and improvement was observed. We received the patient’s consent form about publishing all photographic materials.

Fig. 3
(A) Pathologic evaluation showing hyperkeratosis with regular acanthosis (H&E, ×40). (B) Parakeratosis in the stratum corneum (H&E, ×100). (C) Aggregated neutrophils in the stratum corneum (H&E, ×200). (D) Vascular ectasia with inflammatory cells infiltration in the dermis (H&E, ×100).

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We reviewed the etiology of unilateral psoriasis, and found that genetic mosaicism, nerve denervation, and the Koebner phenomenon have been reported as possible etiologies. Happle1 reported that early loss of wild-type alleles in heterozygous embryonic stem cells can cause a second type of mosaicism. It has been reported that in general, linear or segmented skin lesions caused by early loss of alleles tend to occur earlier and more prominently than symmetric skin lesions, and are resistant to treatment1, 2. In the current case, this etiology was considered less likely because symmetrical psoriasis occurred first, followed by unilateral psoriasis; psoriasis is affected by polygenicity and environmental factors. Moreover, this patient also suffered from poliomyelitis.

Regarding nerve denervation, the second possible etiology, there are cases in which psoriatic lesions have improved in the area corresponding to the ganglion after nerve damage3, 4. The decrease in T cell immunity in the paralyzed area was suggested as a possible mechanism in unilateral psoriasis in a patient with left-leg polio5. There are cases in which psoriatic arthritis have developed except the paralyzed area in patients with poliomyelitis or hemiplegia and immobilization, nerve denervation are suggested as possible mechanisms4, 6. In the current case, the possibility of psoriasis not occurring on the right leg due to poliomyelitis could be related to nerve denervation. However, in our patient, the lesions did not form on the arms and the trunk that have the same condition as that of the left leg, where the lesions had formed. Furthermore, he had papulosquamous lesions on the entire body in the past when he was still suffering from poliomyelitis. From this perspective, the second etiology, i.e., nerve denervation cannot clearly explain this case.

The third possible etiological mechanism is the Koebner phenomenon. Two previous reports of unilateral psoriasis in poliomyelitis have suggested the Koebner phenomenon as an etiology due to unilateral overload and friction7, 8. In our case, the patient walked while bearing the load with his left leg due to paralysis in his right leg. Both his arms shared the load equally. This presentation can be explained by the Koebner phenomenon as the load and friction act mainly on the left leg. Based on the patient’s recall, the Koebner phenomenon was considered to have acted as the triggering and aggravating factor of psoriasis because the scaly papules became more severe after irritation-related contact dermatitis and secondary bacterial infection that occurred post self-dressing.

A study that examined the treatment of linear psoriasis in 30 patients reported that topical treatment was effective9. Our patient also showed improvement after treatment with a combined steroid and vitamin D topical agent. To date, there have been only three reports of unilateral psoriasis in patients with poliomyelitis worldwide (Table 1)5, 7, 8. The Koebner phenomenon is considered the etiological mechanism in our patient because the load and friction act mainly on his left leg and scaly papules became more severe after post self-dressing. Herein, we report a very rare case of a patient with unilateral psoriasis on the left leg and poliomyelitis of the right leg, and present a review of the literature.

Table 1
Review of literature

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