Keywords• leukemia cutis • acute myeloid leukemia • chronic lymphocytic leukemia • chloroma • myeloid sarcoma • granulocytic sarcoma • gingival hyperplasia Summary Leukemia cutis is an extramedullary manifestation of leukemia. The frequency and age distribution depend on the leukemia subtype. The clinical and morphological findings have a wide range of cutaneous manifestations and may present with nodular lesions and plaques. Rare manifestations include erythematous macules, blisters and ulcers which can each occur alone or in combination. Apart from solitary or grouped lesions, leukemia cutis may also present with an erythematous rash in a polymorphic clinical pattern. Consequently, leukemia cutis has to be distinguished from numerous differential diagnoses, i. e. cutaneous metastases of visceral malignancies, lymphoma, drug eruptions, viral infections, syphilis, ulcers of various origins, and blistering diseases. In the oral mucosa, gingival hyperplasia is the main differential diagnosis. The knowledge of the clinical morphology is of tremendously importance in cases in which leukemia was not yet known.

SummaryLichen planus is characterized by lichenoid, polygonal papules with fine white lines, called Wickham striae. Lesions most commonly occur on the limbs and on the dorsal aspect of the trunk. At the same time often leukoplakia of mucous membranes as well as nail disorders are seen.There are numerous variants of lichen planus which can be distinguished from the classical form on the basis of morphology and distribution of the lesions. The typical primary lesion of lichen planus may be replaced by other forms, such as patches, hyperkeratoses, ulcerations, or bullous lesions. Moreover, distribution patterns of these lesions may vary and include erythrodermic, inverse or linear arrangements. In contrast to these numerous clinical features, histologic findings remain characteristic in the variants, so that the diagnosis can be made securely. Differential diagnoses of lichen planus include diverse dermatoses such as bullous pemphigoid or paronychia.

Summary Acquired reactive perforating dermatosis is characterized by umbilicated erythematous papules and plaques with firmly adherent crusts. Histopathological examination shows a typical cup‐shaped ulceration in the epidermis containing cellular debris and collagen. There is transepidermal elimination of degenerated material with basophilic collagen bundles. The etiology and pathogenesis of acquired reactive perforating dermatosis are unclear. Metabolic disorders and malignancies are associated with this dermatosis. Associated pruritus is regarded as a key pathogenic factor. Constant scratching may cause a repetitive trauma to the skin. This pathogenesis may involve a genetic predisposition. The trauma may lead to degeneration of the collagen bundles. Treatment of acquired reactive perforating dermatosis follows a multimodal approach. Apart from the treating any underlying disease, treatment of pruritus is a major goal. Systemic steroids and retinoids, as well as UVB phototherapy are well‐established treatment options. Some patients may also benefit from oral allopurinol.

Keywords• herpes zoster oticus • zoster sine herpete • facial palsy • cranial nerve lesions • acyclovir-corticosteroid therapy SummaryRamsay Hunt syndrome is defined as herpes zoster oticus associated with an acute peripheral facial nerve paresis and quite often with other cranial nerve lesions. The combination of motor, sensory and autonomic involvement leads to a variety of neurological damage patterns, i. e. facial muscle paresis, hearing and balance disorders, sensory problems and disturbances of taste as well as lacrimal and nasal secretion. Additional variability of the clinical picture of Ramsay Hunt syndrome is produced by varying patterns of skin involvement explained by individual anastomoses between cranial and cervical nerves. Knowledge of these findings and an early diagnosis of Ramsay Hunt syndrome are important as prognosis of cranial nerve damage depends on the time at which acyclovir-corticosteroid therapy is started.

Summary Extramammary Paget disease is a rare malignant neoplasm. With regard to the pathogenesis, two prognostically different forms can be distinguished. The primary form of extramammary Paget disease is an in situ carcinoma of the apocrine gland ducts. In contrast, the secondary form is characterized by an intraepithelial spread due to an underlying carcinoma of the skin or other organ systems. Extramammary Paget disease occurs in older patients. The predilection sites include the entire anogenital skin and less often the axillary region. We present five different patients with this disease, thereby demonstrating its variation in clinical morphology. The lesion usually presents as an erythematous sharply defined spot. The polygonal borders, caused by the centrifugal growth of the tumor, may provide a diagnostic clue. The treatment of choice for extramammary Paget disease remains Mohs’ microscopic surgery. However, radiotherapy or topical applications may be alternative treatment options in selected cases. In patients with the secondary form of extramam‐mary Paget disease, treatment of the primary tumor is the main approach.