A Case of Localized Scalp Psoriasis Triggered by Microsporum canis Infected Tinea Capitis
Wenying Hu,Yuping Ran*, Jebina Lama and Xin Ran
M.D. & Ph.D, Department of Dermatovenereology, West China Hospital, Sichuan University, Chengdu, China
Source: Clinical Pediatric Dermatology Journal
We report a case in which patient was initially ill with tinea capitis infected by Microsporum canis later triggered the local scalp psoriasis. Tinea infections always confused with psoriasis, a review of published studies revealed 14 cases of fungal confused with psoriasis.
Scalp; Lesion; Psoriasis; Spores
A 5-year-old girl presented at our clinic with 2-month history of breakage of hair associated with white scaly patches with sizes of the palm on the scalp (Figure 1). She was diagnosed as tinea capitis at the local hospital and was treated with oral terbinafine 125 mg for 18 days and the lesion completely healed. A month after discontinuing medicine, her condition exacerbated then she continued to take oral terbinafine, but the lesion enlarged gradually. A palm size erythema with light yellow scales with broken hair was noticed and she felt intense itch.
Circular and oval tiny spores outside of hairs were observed by direct examination with 15% KOH smear of scales from the scalp (Figure 2A). Fungal culture of scales revealed light yellow filamentous colonies (Figure 2B) and microscopic examination of a slide culture showed large separated avatar spores (Figure 2C), which was consistent with the features of Microosporum canis. DNA of the isolate sequencing was also carried out to confirm the identification as Arthroderma otae (the teleomorph of M. canis), Genomic DNA was extracted using a DNA kit (Omega biotek, USA) and amplification of the intergenic transcribed spacer (ITS) regions flanking the 5.8S region of the rDNA was performed by PCR. The samples were subsequently sent to Invitrogen Life Technologies for DNA purification and bidirectional sequencing. A BLAST search in GenBank using the ITS sequence showed 99% homology to Arthroderma otae (the teleomorph of M. canis).
The sequence has been submitted to the gene data bank and registered under the accession number of KF733019. The patient was diagnosed with tinea capitis caused by M. canis and treated with oral itraconazole 100mg and local application of naftifine and ketoconazole cream once a day for nearly 2 months, but the lesion did not heal completely, white scaly patches was also observed on the scalp (Figure 1B) but direct microscope examination and culture both negative. We carefully interviewed her family history, her mother and maternal grandfather had a history of psoriasis. She was advised for tissue biopsy which showed hyperkeratosis and parakeratosis, acanthosis with elongation of the epidermal rate ridges (Figure 3), indicated the pathology of psoriasis. Periodic acid-Schiff (PAS) and silver staining were both negative. After topical application of 0.03% tacrolimus, the patient was cured (Figure 1C) after 14 days.
Psoriasis is a chronic disease of skin, with prevalence of 2-3% in the general population . Several factors have been identified as being associated either with causation of psoriasis or with triggering exacerbations or remissions, including genetic determinants, racial and regional variation, injury and infection, cigarette smoking, alcohol, diet and other diseases . In our case, first time the patient was diagnosed as tinea capitis at the local hospital and was clinical cured completely by terbinafine, then the tinea capitis recrudescence and triggered psoriasis at the same location. So our patient, the factor of psoriasis was M. canis infection. The mechanism of psoriasis triggered by M. canis infection remains to be studied.
In summary, thirteen cases were tinea infections misdiagnosed as psoriasis, only one case was concomitant psoriasis and tinea corporis. Of the patients  (70%) cases presented with psoriatic atypical signs including erythema, scales were misdiagnosed as psoriasis,  (15%) cases apart from erythema but also pustular were misdiagnosed as pustular psoriasis,  (15%) cases were misdiagnosed as other types of psoriasis.
By reviewing the published papers, we conclude that most cases were tinea infections misdiagnosed as psoriasis because of their analogous presentations (erythema, scales and pustular) and their similar sites, with head, face, trunk and extremities as the most common sites. It doesn't matter with their ages, sex or living areas, the most common fungus in these cases were Trichophyton rubrum and Microsporum gypseum. Itraconazole and terbinafine remain the most effective treatment choices.
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