Pyoderma gangrenosum is a rare, neutrophil‐mediated, auto‐inflammatory dermatosis that wound care specialists must be prepared to recognise. This condition has clinical features analogous to infectious processes. There is no specific diagnostic test and the diagnosis is usually obtained from exclusion. Its early recognition and proper management with prompt initiation of immunosuppressive therapy are essential to improve the quality of life and the prognosis of patients.

Introduction: There are no reports of the density of hair follicles in the scalp of Mexican mestizo population, necessitating the determination of normal references values for this population compared with other ethnic groups. Objective: To determine the average hair follicle count on the scalp in Mexican mestizo population. Materials and Methods: A total of 50 scalp samples (25 men and 25 women) from Mexican mestizo individuals aged between 19 and 60 years, with no clinical evidence of hair disease, obtained by biopsy punch at General Hospital “Dr. Manuel Gea González” were collected over 2 years. The total follicular density, vellus and terminal hair follicles, and the percentage in anagen and catagen-telogen phase were measured. χ² was used as the basic statistical test. Results: The mean number of total hair follicles in our Mexican mestizo population was 23.2 ± 4.2, which is lower compared with Thais, Iranians, and Caucasians. However, the ratio of terminal and vellus hair follicles was higher than in Thais, Caucasians, and African-Americans. The percentage of terminal hairs in anagen phase was lower than in the other populations, and higher in telogen, without exceeding 15%, established as the normal reference value. There was an association between sex and terminal hairs in telogen phase (p < 0.05). The average follicular density per mm² was slightly higher compared with African-Americans and Asians. Women had more terminal hairs than men. Conclusions: The density of total follicles is lower in the Mexican mestizo population compared with Iranians, Thais, and Caucasians. However, the greater number of terminal hairs compared to vellus hairs gives the appearance of greater overall volume. The results of this study can be used as a reference for diseases of the scalp in the Mexican population.

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<b><i>Introduction:</i></b> Spitz nevus is an uncommon, benign melanocytic proliferation that primarily appears on face, trunk or lower extremities of children. This lesion may share clinical and microscopical characteristics with melanoma, making it a diagnostic and management challenge. <b><i>Case Report:</i></b> A 13-year old male presented with an asymptomatic chronic dermatosis located on the third left-hand nail. Cutaneous examination revealed a homogeneous dark brown melanonychia which extended up to the cuticle. Upon dermoscopy, longitudinal bands measuring less than 3 mm wide of heterogeneous colors ranging from light to dark brown, and positive Hutchinson’s sign were observed. <b><i>Discussion/Conclusion:</i></b> We report the second case of a Spitz nevus ungually localized which strongly resembled an ungual melanoma with a positive Hutchinson’s sign upon dermoscopy. Describing the infrequent presentation and location of the Spitz nevus poses an opportunity to establish diagnostic and management criteria in the near future.

We present the case of an HIV-positive patient who developed polymorphous lesions in which the evidence in the skin biopsy corresponds to the diagnosis of bacillary angiomatosis, and further tests proved the pathological agent involved in this case is not the usual Bartonella species, B. henselae and B. quintana, but B. elizabethae. As far as we know, this is the first case of bacillary angiomatosis secondary to this etiological agent.