A detailed classification of myeloproliferative disorders is complex and constantly in flux, with continued advances in immunophenotyping, gene rearrangement studies, fluorescence in situ hybridization, microarrays, comparative genomic hybridization, and laser-based microdissection. Indeed, this chapter was without a doubt the worst chapter in the first edition of this book, so a complete overhaul was needed. Many classification schemes have come and gone over the years. The most…

23.1 Eccrine nevus and apocrine nevus Very rare plaque or patch of hyperhidrosis, onset at birth or early childhood, sometimes with one or many sweat pores. ■ Basaloid hyperplasia of the epidermis sometimes ■ Increased size or number of apocrine or eccrine glands Variation 1. Angiomatous eccrine nevus (eccrine angiomatous hamartoma): blood vessels proliferate along with eccrine glands. Differential diagnosis 1. Increased numbers of sweat glands…

22.1 Trichofolliculoma (see Fig. 22.1A–E ) Uncommon solitary papule on the face (1.44), sometimes with a plugged orifice in which vellus hairs are seen. ■ Large open or closed comedo-like lesion (sometimes resembling a cyst if there is no orifice) into which numerous small hair follicles with trichohyaline granules and vellus hairs open ■ Fibrotic stroma Variations 1. Dilated pore of Winer: solitary 1–3 mm orifice…

21.1 Sebaceous hyperplasia (see Fig. 21.1 ) Common whitish (1.150) to yellowish (1.151) papules, often with a rolled edge or central umbilication, most common on the face (1.145). ■ Enlarged, otherwise normal sebaceous gland, often with a large central orifice ■ Solar elastosis frequent Variations 1. Fordyce spots: enlarged sebaceous glands of the lips (1.74) and rarely on other mucosal surfaces such as the vulva or…

20.1 Freckle (ephelis, plural is ephelides) Very common multiple red – brown macules (1.18) on face (1.44) and shoulders, often genetically inherited in fair-skinned patients , especially those with red hair. Lesions darken easily with sun exposure. ■ Increased melanin in basal layer ■ Normal or decreased number of more active melanocytes ■ No elongation of rete ridges or nesting of melanocytes Differential diagnosis 1. Café-au-lait…

A cyst is a walled-off cavity filled with keratin, mucin, or fluid, and a list of cystic lesions other than those in this chapter appears in Section 1.25. Most true cysts have an epithelial lining, but some, such as the digital mucous cyst or oral mucocele, do not. Cutaneous and subcutaneous cysts are classified on the basis of their location, contents, type of epithelial lining, and…

18.1 Epidermal nevus (linear epidermal nevus) (see Fig. 18.1A,B ) Somewhat common, linear , warty plaque , usually on the extremities, sometimes on trunk, since birth or early childhood, persists indefinitely. Sometimes lesions are more subtle, more macular, or they may have a grouping of papules, or may have pigmentary alterations. They may follow Blashko’s lines, sometimes related to a post-zygotic somatic mosaicism for mutations in…

17.1 Acrodermatitis enteropathica Rare autosomal recessive disorder due to a defect in zinc absorption (mutation in intestinal zinc-specific transporter SCL39A4). Decreased zinc levels can be documented in the serum. Infants develop perioral (1.82), groin (1.55), perianal (1.108), scalp (1.124), and acral eczematous plaques (1.29), with diarrhea (1.49), alopecia (1.4), glossitis (1.139), and secondary infection with bacteria and Candida (13.4). ■ Scale crust often , with confluent…

Panniculitis is inflammation in the subcutaneous fat. The classification of panniculitis is unsatisfactory, as there is considerable overlap between the clinical and histologic features of these diseases. Although many authors categorize a panniculitis as a “septal” panniculitis if it involves primarily the septa between fat lobules and “lobular” if it involves primarily the fat lobule itself, this has limited utility because only one disease can be…

This chapter covers most of the more important parasites, or those with more specific pathologic findings in the skin. Many others are omitted because they either mostly involve deeper tissue, they produce nonspecific findings in the skin unless the parasite is identifiable, or because they are more obscure. 15.1 Leishmaniasis (see Fig. 15.1A–E ) Infection of the skin by protozoa of Leishmania and Viannia species, with…

14.1 Human papillomavirus infection (HPV, viral wart, verruca) (see Fig. 14.1A–H ) Verrucous papules (1.146) due to infection with HPV, of which there are more than 60 subtypes. Warts often bend the dermatoglyphic lines and may have black dots representing thrombosed capillaries in dermal papillae (so-called “seeds” in a “seed wart”). ■ Hyperkeratosis (1.61), papillomatosis , hypergranulosis (1.60) ■ Columns of parakeratosis (1.104), especially over projecting…

13.1 Dermatophytosis (tinea) (see Fig. 13.1A–G ) Very common superficial cutaneous infection by one of the three genera: Microsporum , Epidermophyton , and Trichophyton . Scaly, erythematous plaques, often annular (1.5, hence sometimes called “ringworm”), sometimes pustular, rarely vesicular (1.147). KOH prep shows branching septate hyphae without budding yeast, which may obviate the need for biopsy. ■ Neutrophils sometimes in the stratum corneum, parakeratosis often ■…

12.1 Impetigo (see Fig. 12.1A–D ) Common superficial infection with Staphylococcus aureus and/or Streptococcus pyogenes . Most common in children, especially around mouth, nose (1.95), axilla, or groin (1.55). Honey-colored crusts and an acute onset are typical. Glomerulonephritis (1.66) is a rare complication. ■ Subcorneal pustule filled with neutrophils and sometimes occasional acantholytic cells ■ Spongiosis often (1.132) ■ Dermal perivascular lymphocytes and neutrophils ■ Gram-positive…

11.1 Ichthyosis (see Fig. 11.1A–D ) Although ichthyosis (from Greek ichthys, meaning fish skin; “sauriasis,” from Greek sauros meaning lizard skin, like a dinosaur, as opposed to “psoriasis”) has traditionally been divided into four major groups (the first four listed below), this is an oversimplification. Most present as scaly skin (1.29) at birth or early childhood . There are many syndromes associated with ichthyosis. Ichthyosis vulgaris,…

These are inflammatory diseases involving sweat glands or pilosebaceous units. 10.1 Acne (see Fig. 10.1A–E ) Very common disorder, open comedones (blackheads), closed comedones (whiteheads), red papules , pustules , cysts (ruptured inflamed sebaceous glands without an epithelial lining as in most “true cysts”; 1.25), and nodules. More in teenagers and young adults, more on face and trunk, related to increased keratinization of the infundibulum of…

9.1 Solar elastosis (see Fig. 9.1A,B ) Very common parched or wrinkled skin due to sun damage (dermatoheliosis) with degeneration of connective tissue (increased abnormal elastic tissue and less collagen). ■ Amorphous, fibrous, or globular basophilic material in the dermis ■ Elastic fibers (1.31) become bluish–gray and stain positively with elastic tissue stains ( Chapter 30 ) Variations 1. Nodular colloid degeneration: papule or nodule of…

8.1 Porphyria (see Fig. 8.1A–F ) Uncommon to rare group of porphyrin metabolism disorders. Most of them present as photodermatitis (1.110) with papules or vesicles mostly on sun-exposed skin. Pathology 1. Porphyria cutanea tarda (PCT): most common type of porphyria, uroporphyrin decarboxylase deficiency, most cases acquired and only 20% due to UROD gene mutation, uroporphyrins highly elevated in the urine, “tarda” refers to “late” (adult) onset…

A discussion of granulomas and their differential diagnoses appears in section 1.51. Granulomas can occasionally resemble other non-granulomatous diseases with epithelioid cells (1.38). 7.1 Granuloma annulare (GA) (see Fig. 7.1A–E ) Common idiopathic non-scaly annular plaques (1.5) and erythematous papules, most common on hands (1.56), feet (1.48), elbows (1.32), mostly children and young adults, spontaneously resolve in several years. ■ Epidermis normal ■ Palisading granulomas (histiocytes,…

A list of vesiculobullous diseases appears in section 1.147. Some subepidermal diseases can appear to be intraepidermal when they have re-epithelialized. Usually, the blister will have a smooth base in that case. The following diseases may sometimes produce subepidermal blisters, but are not discussed in this chapter. 1. Erythema multiforme (3.2) 2. Porphyria (8.1) 3. Lichen planus (2.11) 4. Amyloidosis (8.4) 5. Mastocytosis (24.17) 6. Lupus…

The classification of vesicles and bullae are discussed in general in Section 1.147. Many of them are not discussed in this chapter. Some subepidermal diseases can appear to be intraepidermal when they have re-epithelialized. Intraepidermal diseases can also appear subepidermal if the blister blows out into the subepidermal zone or if there is prominent papillary dermal edema. The most common causes of intraepidermal vesicles are eczema…