Dermoscopic image of the hairs in a very early lesion of tinea capitis caused by .

While the initial lesions of tinea capitis are often overlooked due to their small size and numerous hairs emerging from the follicle, it is crucial not to dismiss the partial presence of comma or harpin hairs and black spots.

A case of pyoderma gangrenosum around the urethral meatus aggravated by COVID-19 infection and further worsened due to the development of pyogenic osteomyelitis 8 years after urostomy.

After the infection with COVID-19, pyoderma gangrenosum worsened and further led to necrosis following pyogenic osteomyelitis. Infection is a major exacerbating factor in pyoderma gangrenosum.

Successful treatment with cyclosporine and guselkumab for pityriasis rubra pilaris.

A man with pityriasis rubra pilaris (PRP) showed no improvement in skin symptoms despite treatment with several drugs. The patient was diagnosed as having type 1 PRP. Combination therapy with cyclosporine and guselkumab improved his skin condition.

Progressive vitiligo induced by recurrent melanoma.

A woman had undergone excision for primary melanoma of the left heel and dissection of groin lymph nodes. The recurrent tumor on the lateral left lower leg developed six months ago and the depigmented plaques spread extensively on the left lower limb. The depigmented macules were localized to the left lower limb and were not seen in other areas.

Possible HSP reactivation post-COVID-19 vaccination and booster.

A 45-year-old woman with a history of Henoch-Schönlein (HSP) purpura received COVID-19 vaccination. The patient showed HSP reactivation after COVID-19 vaccination and booster. In HSP, autoimmune memory of vasculitis persists and might be reactivated with COVID-19 vaccination.

Lymphocyte transformation test: The multiple positive results turned to all negative after influenza infection.

Previously positive lymphocyte transformation test (LTT) results changed to negative during influenza infection. As observed in the current article, results of LTT may be influenced by infection; therefore, it is crucial to consider the timing of LTT.