Psoriasis sparing the polio-affected limb: is it merely the koebner phenomenon?

Psoriasis being a common skin condition, atypical forms and unusual localizations of this disease are quite frequently seen. However, psoriasis sparing a polio-affected limb is extremely rare. We report a case of an adult male, who presented with psoriasis distributed all over the body but with almost complete sparing of the polio-affected left lower limb.

What was known?

Psoriasis is a common skin condition which can some times manifest with several atypical forms.

Introduction

Psoriasis is a common skin disease that usually presents with sharply demarcated, erythematous, and scaly plaques that are predominantly located over the extensor surfaces of the body. As the disease is so common in clinical practice, unusual localizations and atypical presentations are quite frequently encountered.[1] Recognition and proper interpretation of such unusual presentations of psoriasis may help us to better understand the pathomechanisms of psoriasis.[2] Here, we present a case of psoriasis vulgaris where there was almost complete sparing of the polio-affected left lower limb.

Case Report

A 29-year-old male presented with 7 years history of asymptomatic, erythematous, scaly, plaque lesions over both elbows, extensor aspects of both forearms, right knee, and the extensor aspect of the right leg. It was revealed by the patient that his left lower limb had been polio affected in childhood. Conspicuously, the polio-affected left leg was almost completely spared of psoriatic lesions [Figure 1]. Both his upper extremities were equally affected, almost in a symmetrical fashion. His hair, nails, and oral mucosa were not involved. There was no joint involvement. There was no obvious history of any injury at the site of the present lesions. There was no history of psoriasis or any other skin disease in the family.

Figure 1

Psoriatic lesions on the right leg the polio-affected left leg was almost completely spared

Systemic examination did not reveal any abnormality. Serum was negative for anti-human immunodeficiency virus antibodies and routine laboratory investigations were within normal limits. Histopathology showed features of parakeratosis, spongiosis, regular elongation of rete ridges, and dilated tortuous capillaries, with inflammatory infiltrate in the papillary dermis, a picture that was consistent with psoriasis [Figure 2].

Figure 2

Histopathological features consistent with psoriasis (H and E, original magnification ×100)

The patient was treated with a combination of topical steroids and keratolytics and adviced to come for regular follow-up.

Discussion

Psoriasis is one of the most common chronic, inflammatory, hyperproliferative skin disorders of man. Its etiology and pathogenesis have for long fascinated dermatologists, pathologists, and biologists alike. It commonly presents as sharply demarcated, erythematous and scaly plaques, predominantly over the extensor surfaces of the body. Atypical forms and unusual localizations of the disease are quite frequently seen. However, psoriasis sparing the polio-affected part of the body is extremely rare. In the only such report that we could find in the literature, the polio-affected right lower limb of a patient was spared of psoriatic lesions.[3] This was attributed to the Koebner response, with the increased weightbearing by the non-polio-affected limb and the consequent friction being held responsible for the preponderance of lesions on that limb. In our case also, friction and increased weightbearing on the non-polio-affected right lower limb may have been the reasons for the preponderance of psoriatic lesions on that limb.

The Koebner response may be a marker for a subset of psoriatic patients. For these patients, injury is a pathway to psoriasis.[4] The predominance of infiltrating cytotoxic T-cells found in the epidermis and dermis in Koebner-positive skin is activated by heat shock proteins and directly induce lytic changes in keratinocytes. Alternative explanations include degranulation of mast cells and release of proteases by macrophages.[5]

Psoriasis is a disease that allows us to study neuroectodermal – mesenchymal interactions from different angles. Though neurogenic factors are involved in psoriasis pathogenesis, they are not considered here as they are reported to be relevant only in diseases with sensory impairment. In our patient, it is necessary to explore whether the Koebner response alone was the reason for the psoriasis lesions sparing the polio-affected limb or if there were other factors also playing a role in this regard. Despite extensive search of the literature, we could not come across any other plausible explanation for this intriguing presentation of psoriasis.

What is new?

Psoriasis sparing the polio affected limb is an unusual and hither to unreported finding.