Many faces of Koebner phenomenon in psoriasis

Introduction

Koebner (isomorphic) phenomenon is defined as a non specific skin stimulus eliciting a disease skin reaction.[1] Various diseases exhibiting this interesting phenomenon include psoriasis, lichen planus, erythema multiforme, vitiligo, warts, molluscum contagiosum, pyoderma gangrinosum, pityriasis rubra pilaris and so on.[1] The prototype of the isomorphic response, however, occurs in psoriasis and has been studied more extensively in this disease.[1] We have recently observed two unusual causes of koebner phenomenon in psoriasis.

Patient 1: A 33 - year -old male patient presented with a 26 - year history of keloid and psoriasis. About 26 years previously, he developed keloids and psoriasis spontaneously. He described that healing of psoriasis at few places resulted in keloid formation and later psoriasis relapsed mainly on the top of the keloids, in addition to other sites like scalp palms and soles. He noted remissions and relapses of psoriasis several times, but the lesions of keloids remained persistent. In the past, he received intralesional triamcinolone and topical steroids for his keloidal lesions and methotraxate orally (total cumulative dose 635 mg) for relapses of psoriasis. At the time of presentation, he was not receiving any treatment for last 6 months. He had 16 typical keloidal growths distributed over chest, shoulder, knees and lower back. This time the lesions of psoriasis spontaneously appeared about 2 months back.He complained of constant pain and irritation in all the keloidal lesions. In addition, he had psoriatic plaques distributed on the plams, soles, scalp and on the top of all the keloidal growths. Surprisingly, the areas adjacent to the keloid and non - keloidal skin of the trunk and extremities were free of psoriatic lesions [Figure - 1]. Topical therapy, in the form of coal tar combined with sun exposure, resulted in resolution of psoriasis, though the keloids persisted.

Patient 2: A 67- year -old man presented with lesions of herpes zoster in thoracic region, which, at the time of presentation, were in the healing stage. The healing was associated with development of scaly lesions at the site of eruption [Figure - 2]. The patient had psoriasis several times in the past 2 - years; he however, was in remission for last 5 months. He received treatment topical medications for psoriasis in the past.

Patient complained of pain and itching in the lesions of herpes zoster. The lesions of psoriasis closely followed with the appearance of the crusting in the herpes zoster lesions. He also developed few guttate lesions of psoriasis elsewhere on the trunk. The lesions were erythematous, scaly, slightly raised, round to oval in shape and less than 1 - cm in size.

Discussion

The first had lesions of psoriasis and keloids for more than 26 - years. He however, was not aware of which disease came first, though he gave a definite history of some lesions of psoriasis healing with keloid formation and,later the recurrence of psoriasis selectively on the top of the keloids. Various reported diseases provoking isomorphic phenomenon in psoriasis include acne, insect and animal bites, burns,contact dermatitis, lichen planus, miliaria, photosensitivity, pityriasis rosea, tattoo, vasculitis, vitiligo, lymphagitis, furuncle, herpes zoster, syphilis, leprosy and varicella.[1],[2],[3],[4],[5],[6],[7],[8] On the other hand, dermatologic disorders reported to cause keloid formation include dissecting cellulitis of the scalp, acne vulgaris, acne conglobata, hidradenitis suppurativa, pilonidal cyst, foreign - body reaction, burns, chicken pox, folliculitis, herpes zoster, vaccinia and small pox.[9],[10] Some connective tissue diseases such as Ehler - danlos syndrome and scleroderma have also been reported to be associated with keloid formation.[10] Obviously, the keloid does not get a place in the long list of dermatologic disorders causing koebner phenomenon in psoriasis does not get a place in the long list of diseases causing keloid formation. As the patient had pain and irritation in the keloid (not itching), the possibility of scratching as precipitating factor can be eliminated. Moreover he also had lesions on the unapproachable sites like over the back.

Transforming growth factor (TGF) - β is a cytokine that enhances extracellular matrix production by a variety of cells in vivo and in vitro. It is associated with increased procollagen gene expression in keloids.[11] The production of TGF - β has been found to be increased in psoriasis.[12] TGF - β along with other growth factors regulate keratinocyte proliferation/ differentiation process[13] and, it has been shown that TGF - β 1 levels are increased in psoriatic plaques and correlated with Psoriasis area severity index (PASI) score.[14] It Is possible that increased levels of TGF - β in keloidal lesions are responsible for localization of psoriasis in the kelodis. Similarly, increased expression of TGF - β in psoriatic plaques might be responsible for development of keloid formation on the healing of psoriatic plaques.

The koebner phenomenon in our second patient is less strange. Literature search revealed few reported patients with development of psoriatic lesions at the site of lesions of herpes zoster as well as varicella.[6],[7],[8] Farber et al[15] proposed a role of neuropeptides in the etiopathogenesis of psoriasis. They suggested that neurogenic inflammation mediated by agents such as substance P could be the underlying mechanism. Substance P also plays important role in the pain associated with herpes zoster. It is an endogenous neuropeptide that acts as a chemomediator of nociceptive impluse from periphery to central nervous system. The pain associated with herpes zoster responds to capsacin, which acts by depleting substance p from nerve endings. There are evidences that viral infection could potentiate the effect of substance P by decreasing the degradation of its breakdown enzyme, neural endopaptide.[7] This could be the possible explanation of koebner phenomenon in psoriasis occurring at the site of healing herpes zoster lesions. In conclusion, the first case is the first report of an association of keloids and psoriasis, i.e. keloid appearing at the site of healing psoriasis and recurrence of psoriasis selectively on the top of the keloids. The second case further documents the rare occurrence of koebner phenomenon in herpes zoster.