Chapter 253: Skin Disorders: Extremities

This chapter focuses on common disorders of the hands, feet, and extremities and is organized into the following subgroups: ulcers, inflammatory conditions, cutaneous infections, and vascular cutaneous conditions.

VENOUS STASIS DERMATITIS AND VENOUS LEG ULCERS

The vast majority of leg ulcers are venous stasis ulcers resulting from chronic venous insufficiency.¹ Chronic venous insufficiency is usually caused by episodes of phlebitis or varicose veins, both of which damage venous valves. This results in poor venous return from the lower extremities, leading to increased hydrostatic pressure and lower extremity edema and stasis dermatitis.

Dependent edema, erythema, and orange-brown hyperpigmentation characterize early stasis dermatitis. The medial distal legs and the pretibial leg are the areas most frequently affected. More chronic and severe cases may have bright weepy erythema and even ulceration (Figure 253-1). Pruritus is common. Cellulitis and lymphangitis may complicate stasis dermatitis. The presence of honey-colored crust and pustules suggests secondary bacterial infection.

Stasis ulcers often begin within areas of stasis dermatitis. The bilateral malleoli and the medial aspect of the calf are the most common sites of involvement. Diagnosis is clinical. With acute exacerbation, secondary infection is common. Table 253-1 lists the differential diagnosis of leg ulcers. Certain disorders, such as arterial ulcerations, pyoderma gangrenosum, and polyarteritis nodosa require immediate attention. If peripheral pulses are diminished or absent, obtain vascular blood flow studies to exclude arterial ulcers. If the patient reports a rapidly developing ulcer that began as a pustule or erythematous nodule and has violaceous overhanging borders, suspect pyoderma gangrenosum. If the diagnosis is in question, consult with a dermatologist.

Treatment of venous stasis dermatitis and ulcers begins with leg elevation and the use of support stockings. Weeping eruptions should be treated with an astringent compress. A low- to mid-potency topical steroid, such as fluocinolone acetonide 0.025% or hydrocortisone 2.5% ointment, should be applied twice a day until erythema, scale, and pruritus resolve. Oral antihistamines, such as diphenhydramine or hydroxyzine, should be used for pruritus and for nighttime sedation. Secondary bacterial infection should be treated with cephalexin, dicloxacillin, or ciprofloxacin for 7 to 10 days. Topical neomycin, antihistamine creams, and anesthetic creams should be avoided because they may complicate the condition with allergic contact dermatitis. Cellulitis or lymphangitis may require hospitalization for IV antibiotics. Otherwise, follow-up should be arranged with a chronic wound care team.¹

PYODERMA GANGRENOSUM

Pyoderma gangrenosum is a recurrent cutaneous, necrotizing, and noninfective ulceration of the skin that most commonly occurs in women between 30 and 50 years of age.² Most cases are associated with underlying disease, such as inflammatory bowel disease, rheumatoid arthritis, and myeloproliferative disorders.³

The classic lesion of pyoderma gangrenosum begins as a superficial pustule or erythematous nodule that expands into a large painful ulcer on the lower extremity with a purulent base and irregular, undermined borders and gun metal gray hue (Figure 253-2). There is no associated lymphadenopathy. Up to 50% of patients develop lesions at the sites of trauma, such as surgery sites or injection sites, or after blood drawing.² A history of multiple surgical debridements with sterile cultures should suggest a potential diagnosis of pyoderma gangrenosum.

The diagnosis is clinical and one of exclusion. Search for associated conditions, such as inflammatory bowel disease and myeloproliferative disorders. The onset of new skin lesions or ulcers at previous sites of trauma can also be helpful in identifying pyoderma gangrenosum.⁴

Treatment of the underlying disorder and corticosteroids, either topical, intralesional, or combined local and systemic, are the standard therapy for pyoderma gangrenosum. Resistant disease may require adjunctive systemic therapy with immunosuppressive or cytotoxic agents.⁴

DIABETIC AND NEUROPATHIC ULCERS

Most patients with diabetic foot ulcers have coexistent diabetic neuropathy.⁵ Other causes of neuropathic leg ulcers are much rarer and include leprosy, tabes dorsalis, medications, and spinal cord lesions. In most patients with foot ulcers, one will note a triad of neuropathy, deformity, and trauma. Neuropathy leads to atrophy of the intrinsic muscles of the foot, collapse of the arch, and loss of stability of the metatarsal-phalangeal joints. The musculoskeletal alterations result in abnormal pressure points and greater friction on the foot during ambulation. Lack of sensation allows for repeat injury. The most common source of trauma is inappropriate footwear.⁶

Classic locations for neuropathic ulcers are the plantar surface underlying the first and fifth metatarsal heads, great toe, and heel. Ulcers are usually asymptomatic and "punched out" with a thick rim of surrounding callous (Figure 253-3). However, patients may complain of burning, numbness, itching, or paresthesias. The architecture of the foot is also altered, with flexed toes and prominent metatarsal heads secondary to neuropathy of the intrinsic muscles of the foot. Hypo- or anhidrosis from autonomic impairment may lead to dryness and fissuring of the surrounding skin. The diagnosis is clinical.

Patients with vascular insufficiency should be referred to a vascular specialist for further evaluation. A diabetic foot infection is diagnosed clinically when there are systemic signs of infection, purulence, or multiple signs of local inflammation (redness, warmth, pain, tenderness, or edema).⁶ Osteomyelitis is suggested by the ability to probe bone with a blunt, sterile, stainless-steel probe and should be confirmed with imaging.

Treatment includes offloading or redistributing the pressure off the wound, maintenance of a moist wound environment, debridement of nonhealing tissue, and treatment of infection. Soft tissue infections can be treated for 7 to 14 days in an outpatient setting with oral cephalosporin, clindamycin, amoxicillin/clavulanate, or fluoroquinolones.⁷

More severe ulcers or those with associated cellulitis or osteomyelitis require admission and treatment with IV antibiotics for 4 to 6 weeks, such as cefotetan, ampicillin/sulbactam, or clindamycin and a fluoroquinolone. Vancomycin should be given if methicillin-resistant Staphylococcus aureus is suspected. Further discussion is provided in chapter 224, "Type 2 Diabetes Mellitus"; Table 224-4 lists the various cutaneous manifestations of diabetes.

BURULI ULCERS

Buruli ulcer is a new emerging disease and the third most common chronic mycobacterial infection in humans after tuberculosis and leprosy.⁸ Buruli ulcers are rapidly growing ulcers caused by the acid-fast bacillus, Mycobacterium ulcerans. It is usually confined to the tropical areas, with the highest rate in sub-Saharan Africa, but reports have come from subtropical and nontropical nations, including Australia, China, and Japan.⁹

M. ulcerans is an environmental saprophyte that is present on lush vegetation in swampy areas.¹⁰ It infects humans after abrasions come into contact with contaminated soil, water, or vegetation.¹⁰ M. ulcerans produces mycolactone, a cytotoxic lipid and necrotizing immunosuppressive polypeptide toxin that induces both apoptotic and necrotic changes in fibroblasts, lipid cells, macrophages, and keratinocytes.¹¹ Buruli ulcers are painless, and it is thought mycolactone damages the peripheral nerves.¹²

The Buruli ulcer begins as an erythematous nodule approximately 8 weeks after inoculation that eventually ulcerates. The lesions develop on exposed parts of the body, especially on the extremities and face. The resulting painless ulcer has a deep white or yellow necrotic base and undermined edges, as well as edematous surroundings (Figure 253-4). Regional lymphadenopathy and systemic symptoms are minimal to absent. Without treatment, ulcers may spontaneously heal within 6 to 9 months, or they may spread rapidly, causing extensive deformity.

Smears from the base of the ulcer or biopsy specimens should be cultured and examined for acid-fast bacilli. Visible growth by culture requires 6 to 8 weeks, and its success rate is low. Polymerase chain reaction performed on a fresh biopsy is the best method for early diagnosis. Surgical excision is the treatment of choice. Local heating and hyperbaric oxygen also promote healing.¹³ Antimycobacterial treatment is often ineffective.¹³ The World Health Organization recommends rifampin and streptomycin dual therapy for 8 weeks. New skin lesions may develop during antimicrobial therapy, and this is known as "paradoxical reactions."⁸

CUTANEOUS LEISHMANIASIS

Cutaneous leishmaniasis is transmitted by the bite of the sand fly, which is infected by protozoan parasites of the genus Leishmania. In tropical and subtropical regions, leishmaniasis is one of the most common and serious infectious diseases. It is endemic in North Africa, the Mediterranean, the Middle East, India, Central Asia, and Central and South America. Reactivation of latent leishmaniasis can occur in immunosuppressed, human immunodeficiency virus, malnourished, or organ transplant patients.¹⁴ There are many varieties of cutaneous leishmaniasis. The typical cutaneous ulcer usually occurs on unclothed skin, is painless, varies in size from 0.5 to 3.0 cm in diameter, and is covered with an exudative crust (Figure 253-5). Diagnosis is clinical but can be confirmed with culture, biopsy, or polymerase chain reaction test. Most lesions heal spontaneously over several months.¹⁵

HAND AND FOOT DERMATITIS

Hand and foot dermatitis simply means inflammation of the skin of the hands and/or feet. This nonspecific term is used for several more specific disorders (Table 253-2). The most common causes are contact dermatitis (allergic and irritant), dyshidrosis, and atopic dermatitis. Most contact dermatitis is caused by irritants as opposed to allergens. Atopic dermatitis affects children, usually before 5 years of age, and 2% to 3% of adults.¹⁶

Common irritants include soaps, detergents, friction, frequent hand washing, and cold, dry air, resulting in erythema, scaling, and fissuring. Strong irritants like an acid or alkali cause immediate burning, followed by erythema, vesiculation, and bullae formation.

Common allergens include poison ivy/poison oak, nickel, chromate, rubber components of gloves and shoes, dyes in leather and socks, and dichromates used in tanning leather. In acute allergic contact dermatitis, erythema with papules, vesicles, and/or bullae is present. Pruritus is intense, and excoriations are present. Distribution is the most helpful clue to aid in diagnosis. When the hands or feet are involved in allergic contact dermatitis, the eruption tends to be present on the dorsal surfaces, sparing the palms, soles, and web spaces. The thick stratum corneum of the palms and soles prevents penetration of potential allergens. Distribution with linear streaks suggests a plant allergy such as rhus (poison ivy or oak) hypersensitivity (Figure 253-6). Sharp demarcation of footwear indicates a reaction to a component of the patient's shoes.

Dyshidrosis initially begins as very small, deep-seated, pruritic vesicles on the lateral aspects and the volar surfaces of the palms and soles (Figure 253-7). The dorsal surface of the distal phalanges may also become involved. There is no erythema. Over time, the vesicles may form pustules or desquamate to leave small collarettes of scales. In chronic cases, erythema and scales become more prominent and may be difficult to distinguish from other forms of hand and foot dermatitis.

Atopic dermatitis is part of the "atopic triad" consisting of dermatitis, asthma, and allergic rhinitis.¹⁷ Atopic dermatitis of the hands and feet often presents as erythematous, pruritic, scaly patches with prominent involvement of the dorsal surfaces as well as the palms and soles. Chronic atopic dermatitis will also have hyperpigmentation and lichenification and fissuring. Often, other areas of the body are involved. Common areas of involvement include the antecubital and popliteal fossae, posterior neck, and wrists and ankles (Figure 253-8).

The diagnosis is clinical. Differentiating contact dermatitis (allergic and irritant) from dyshidrosis and atopic dermatitis can be extremely difficult. More than one disorder may be present at a time, such as atopic dermatitis complicated by irritant dermatitis. Always consider a fungal infection (see later section "Tinea Pedis and Tinea Manuum"), and a potassium hydroxide preparation can exclude this possibility. A biopsy cannot differentiate between the different types of dermatitis. See Table 253-3 for definitions of terms in superficial cutaneous fungal infections and Table 253-4 for causes of superficial cutaneous fungal infections. Dermatologic consultation is often necessary for specific diagnosis.

Treatment is the removal of offending agents. Antihistamine, anesthetic, antibiotic, and anti-itch creams should be stopped because they may cause a second allergy. Lubricate with petroleum jelly, or thick ointments with a petroleum base, frequently and liberally.

For acute eruptions with vesiculation, use aluminum acetate, two to three times per day. Mix one aluminum acetate powder packet or tablet with 1 pint of water, and then apply with a towel or gauze to the affected area for 15 to 20 minutes. Use a high-potency topical corticosteroid, such as clobetasol ointment, twice a day, after the compress. Hydroxyzine, 25 to 50 milligrams up to four times a day, can relieve itching.

In severe cases with debilitating eruptions, systemic glucocorticoids are indicated. For poison ivy or oak, give oral prednisone, 60 milligrams/d, for 2 to 3 weeks. Shorter courses of prednisone can result in relapse.

Treat chronic eruptions with high-potency topical corticosteroids two to three times a day. Ointments are preferred because they help with lubrication. Systemic glucocorticoids should be avoided in chronic cases and atopic dermatitis. Although systemic steroids may provide temporary relief, rebound activity after cessation is common.

PSORIASIS

Psoriasis vulgaris or plaque-type psoriasis may involve only the palms and soles but often extends to other areas, especially the elbows, knees, scalp, umbilicus, and gluteal cleft (see chapter 251 for more discussion). If pustules are present, the disorder is called pustular psoriasis. Peak ages of onset are between 20 and 30 years old and between 50 and 60 years old.

Psoriasis is an inherited disease in which the principal abnormality is believed to be an abnormal T lymphocyte–driven immune process. These altered T cells are believed to secrete cytokines that shorten the keratinocyte cell cycle and produce arthropathy.

Psoriasis is characterized by discrete plaques of erythema, scales, and fissures on the extremities (Figure 253-9). Extensive disease may extend over the entire palms, soles, and dorsal surfaces of the hands or feet (Figure 253-10). Onycholysis (separation of the nail plate from the nail bed), nail pits, and yellow discoloration of the nails help support the diagnosis of psoriasis (Figure 253-11).

In pustular psoriasis of the palms and soles, erythema, minimal scale, and numerous sterile pustules are seen. The pustules are in various stages of evolution from small pustules to larger confluent "lakes of pus" to crusts to rings of scale (Figure 253-12). Pustules are most commonly seen bilaterally on the instep of the foot and the thenar and hypothenar eminences of the hands.

Complete examination of the skin focusing on the sites commonly affected by psoriasis, including the elbows, knees, scalp, lower back, gluteal cleft, umbilicus, and nails, may reveal other areas of involvement to aid in diagnosing psoriasis. If no other psoriatic plaques are noted, differentiation from hand and foot dermatitis can be difficult (Table 253-5). A biopsy may be helpful in this instance. A potassium hydroxide examination should be performed to exclude a dermatophyte infection. Bacterial and viral cultures should be obtained when disease is pustular and localized to one area.

Initial treatment includes the use of a high- or ultrahigh-potency topical corticosteroid such as fluocinonide, clobetasol propionate, or betamethasone dipropionate ointment. Encourage liberal use of white petrolatum-based topical emollients. Do not prescribe systemic steroids because of the risk of rebound or induction of pustular psoriasis. The disease is chronic and slow to respond to treatment. Arrange follow-up with a dermatologist.

ERYTHEMA NODOSUM

Erythema nodosum is an inflammatory eruption of the subcutaneous fat. It has many possible causes (Table 253-6) and is idiopathic in nearly half of cases. All age groups can be affected.

Tender, warm, ill-defined erythematous nodules characterize erythema nodosum (Figure 253-13). Nodules are most commonly seen on the pretibial area of the lower extremities, although the extensor aspects of the arms and torso can occasionally be involved. Ulceration is not a feature and suggests another diagnosis. Nodules can persist for weeks.

The diagnosis is clinical and should include evaluation for possible causes (Table 253-6). If the diagnosis is unclear (Table 253-7), refer for a biopsy.

Treatment is symptomatic, with leg elevation and nonsteroidal anti-inflammatory drugs. Treat the underlying cause. Refer refractory cases to a dermatologist.

LICHEN SIMPLEX CHRONICUS, CORNS, AND CALLUSES

Lichen simplex chronicus, corns, and calluses are all thickenings of the upper layer of the skin (stratum corneum) in response to chronic friction and scratching. Most commonly, ankles, lower extremities, neck, scrotum, and vulva are involved. When friction occurs in the absence of pruritus and is distributed over a large area, a callus is formed. When the same frictional forces occur over a localized area of the foot, a corn is formed. Calluses and corns are most commonly located on the feet.

Lichen simplex chronicus presents as one or several intensely pruritic, well-demarcated plaques, with lichenification because of chronic scratching and rubbing (Figure 253-14). Erythema, hyperpigmentation, and excoriations are also present. Scale is minimal. The ankles, shins, dorsal feet, and hands may be affected.

Calluses and corns present as thickened plaques at areas of repetitive trauma. Corns form firm, dome-shaped papules with translucent central cores on the dorsal, lateral, and interdigital toes (Figure 253-15).

Diagnosis is clinical (Table 253-8). A potassium hydroxide examination can be helpful to rule out a dermatophyte infection. If the diagnosis is uncertain, refer for a skin biopsy. Paring of warts reveals punctuate thrombosed capillaries, which are not found in calluses or corns.

For lichen simplex chronicus, interrupting the scratch–itch cycle is the most important aspect of treatment. High-potency topical corticosteroids such as fluocinonide or clobetasol ointment should be applied to the plaque two to three times a day. Oral antihistamines help for pruritus.

Paring and keratolytics, such as salicylic acid, are first-line treatments for corns and calluses, as well as proper footwear and medical management.¹⁸ For further treatment, refer to a podiatrist or dermatologist.

DERMATITIS HERPETIFORMIS

Dermatitis herpetiformis is a cutaneous manifestation of gluten sensitivity. It is most common in individuals of northern European descent.¹⁹ Often, there is familial involvement, and there is almost universal association with HLA-DQ2 or HLA-DQ8, located on chromosome 6, with close relatives being affected by either dermatitis herpetiformis or celiac disease.²⁰

Granular deposits of immunoglobulin A are found at the dermal–epidermal junction of all patients with dermatitis herpetiformis. These deposits are believed to attract neutrophils, which induce vesicle formation. The presence of immunoglobulin A antibodies to tissue transglutaminase is also highly sensitive and specific for the disorder.²¹

Extremely pruritic vesicles, papules, or urticarial plaques are symmetrically distributed on extensor surfaces of the extremities, back, and buttocks (Figure 253-16). Chronic scratching may result in excoriations and lichenification in these locations. Approximately 20% of patients will have clinical evidence of malabsorption.²²

The diagnosis is supported by clinical, biopsy, and laboratory findings (Table 253-9). Diagnosis and treatment require dermatology referral.

Treatment for dermatitis herpetiformis includes oral dapsone and a gluten-free diet. Oral dapsone relieves pruritus within 72 hours of beginning therapy. Systemic steroids are ineffective.

FISH TANK GRANULOMA

Fish tank granuloma is an infection by Mycobacterium marinum that classically presents as an ulceration or suppurating abscess with a line of nodules along the corresponding lymphatic drainage. It most commonly affects individuals frequenting swimming pools or who clean fish tanks.²³ M. marinum is found in all aquatic environments, including fresh, salt, and brackish water, swimming pools, and lakes. Infection requires exposure of abraded or traumatized skin to a contaminated environment.²³

Two to three weeks after exposure, a solitary nodule or pustule forms. The skin breaks down into a crusted ulcer, suppurative abscess, or verrucous nodule (Figure 253-17 and Table 253-10). Often, multiple lesions will form along the course of the draining lymphatics, with minimal lymphadenopathy.²⁴

The history and clinical features should evoke suspicion, which should be confirmed by culture. A clinical distinction can also be made from cat-scratch fever and primary inoculation tuberculosis by noting an absence of significant lymphadenopathy in patients infected with M. marinum. Other diagnoses can be excluded by a skin biopsy.

M. marinum is sensitive to rifampicin, clarithromycin, tetracyclines, and trimethoprim-sulfamethoxazole.^24,25 After sensitivity testing, antibiotic therapy is usually continued for approximately 6 weeks, typically under direction of an infectious disease specialist.

CUTANEOUS LARVA MIGRANS

Cutaneous larva migrans is a cutaneous eruption caused by the migration of hookworm larvae within the epidermis. The disease is most commonly found in tropical and subtropical climates where people walk barefoot in environments contaminated with animal feces.

Erythematous and serpiginous tracts are formed as the larva migrates within the skin (Figure 253-18). The patient will often complain of pruritus. A CBC may demonstrate peripheral eosinophilia; patients are otherwise well. Diagnosis is clinical. A single oral dose of albendazole or ivermectin is usually effective.²⁶

PLANTAR WARTS

Plantar warts are a common infection of children caused by the human papillomavirus. They may be acquired through direct contact with infected individuals or indirectly through contaminated surfaces. Most warts will spontaneously regress within 1 to 2 years.

Plantar warts occur on the sole of the foot, especially over pressure points, as thickened papules and plaques that disrupt normal skin lines (Figure 253-19). Black dots, representing thrombosed capillaries, will often cover the surface or become evident upon superficial paring. Diagnosis is clinical (Table 253-11).

Initial treatment is topical salicylic acid. Cryotherapy and electrodesiccation are other options.

TINEA PEDIS AND TINEA MANUUM

Tinea pedis, or athlete's foot, is a fungal infection of the feet, and tinea manuum involves the hand. Tinea manuum is often unilateral and associated with tinea pedis. Often, if one hand is involved, both feet are involved as well. It is unclear why the other hand is spared in this "two foot, one hand" type of fungal infection. Tinea pedis is very common and usually begins in early adulthood. It is rare in children. Predisposing factors include hot, humid weather, excessive sweating, and occlusive footwear. Trichophyton rubrum, Trichophyton mentagrophytes, and Epidermophyton floccosum are the most common organisms involved. T. mentagrophytes is most likely to cause inflammatory bullous tinea pedis. Infections are transmitted from person to person or from animal to person via fomites or direct contact.

There are three main clinical types: interdigital, hyperkeratotic (scaling), and bullous. Interdigital tinea pedis is the most common and is characterized by maceration and scale in the web spaces between the toes. Ulceration may even be present in severe cases that have a secondary infection with bacteria or yeast (Figure 253-20).

Hyperkeratotic, chronic, dry scales involve palms and soles, with little, if any, inflammation. When involving the medial and lateral aspects of the feet, it is called "moccasin" tinea (Figure 253-21). Nails may be affected.

Bullous tinea consists of an acute, painful, erythematous and pruritic vesicular eruption on the palms or soles (Figure 253-22). Toenails and web spaces are usually not involved.

Diagnosis is based on clinical examination and identification of fungal elements on a potassium hydroxide preparation or with fungal culture. If the clinical examination is highly suspicious for a fungal infection, empiric therapy is reasonable. If the diagnosis is uncertain, obtain scrapings for fungal cultures before beginning therapy because culture results (whether positive or negative) can help the follow-up physician choose the most appropriate therapy.

Although a potassium hydroxide examination appears to be a simple test, it is often difficult for clinicians to perform and interpret (see Table 248-6). Scraping of scale can also be sent to the laboratory for potassium hydroxide examination and fungal culture. Hyphae appear as light-green, thin strands that cross over cells and have branches (see Figure 248-1).

Treat interdigital and hyperkeratotic (nonbullous) tinea with topical antifungals, such as clotrimazole, miconazole, ketoconazole, or econazole cream. Apply to affected areas twice a day and continue for 1 week after clearing. Although econazole cream is expensive, it is preferred for interdigital tinea pedis because it has antibacterial properties to treat secondary bacterial (often Corynebacterium) infection. Topical terbinafine cream is a nonprescription alternative and is applied once a day. Topical agents do not treat nail infections. For treatment of onychomycosis, an oral agent such as itraconazole, fluconazole, or terbinafine is needed, but this treatment is best managed by the primary care physician or dermatologist.

Bullous tinea pedis often does not respond to topical treatment. For mild cases, a topical agent can be tried initially. In more severe cases, oral antifungal treatment is necessary. Itraconazole, 200 milligrams PO each day for 14 days, or terbinafine, 250 milligrams PO each day for 14 days, is effective. The prescribing physician should be familiar with the potential drug interactions and the uncommon, but serious, side effects (hepatotoxicity and erythema multiforme/toxic epidermal necrolysis) before prescribing these medications. Baseline liver function studies should be obtained when prescribing terbinafine.

Hands and feet should be kept as dry as possible. After bathing, web spaces should be thoroughly dried. Socks should be changed any time they become wet with sweat. If the eruption is not clear in 4 to 6 weeks, dermatology referral is needed. The disease is chronic, and recurrences are common.

ROCKY MOUNTAIN SPOTTED FEVER

Rocky Mountain spotted fever is a potentially fatal multisystem illness caused by Rickettsia rickettsii. Symptoms begin 2 to 14 days after an infected tick bite. The organism disseminates through the bloodstream and invades the vascular endothelium, causing a necrotizing vasculitis. Fever, headache, and myalgias develop about 1 week after exposure. The rash in classic Rocky Mountain spotted fever is evident 2 to 5 days after the onset of fever and other symptoms. In most patients, some type of rash develops during the illness, but about 10% never develop a rash.²⁷

The rash first appears on the wrists and ankles and rapidly spreads to the palms and soles (Figure 253-23, A and B). As the rash moves centrally, the proximal extremities, trunk, and face become involved. The skin lesions at the onset are described as discrete macules or maculopapules that blanch with pressure. The initial lesions evolve into petechiae over 2 to 4 days, fade slowly over 2 to 3 weeks, and heal occasionally with hyperpigmentation. Rarely, the petechiae may coalesce into ecchymotic areas with eventual gangrene of the distal extremities, nose, ear lobes, scrotum, and vulva—purpura fulminans. Treatment for adults is doxycycline, 100 milligrams PO twice a day; for children under 45 kg with permanent teeth, treatment is doxycycline, 2.2 milligrams/kg twice a day. Doxycycline does not cause staining of permanent teeth. For further discussion of the treatment of this and other tickborne diseases, see chapter 160, "Zoonotic Infections."

PURPURA

Purpura is visible hemorrhage into the skin or mucous membranes. Small, flat lesions are petechiae, and large, flat lesions are ecchymoses. Palpable purpura has a physically palpable elevation. Diverse abnormalities of coagulation and blood vessel function lead to hemorrhage into the skin. These include abnormalities of platelet number or function, procoagulant defects, poor dermal support of vessels, increased pressure within vessels, trauma, vascular inflammation, and vascular occlusion.

The cutaneous and systemic causes of purpura are broad. Nevertheless, some broad generalizations can be made. Large ecchymoses generally signify coagulation defects or trauma and may be associated with signs of external or internal bleeding. Petechiae are often associated with thrombocytopenia and bleeding in other locations. Palpable purpura and persistent, localized purpura suggest vasculitis (Figure 253-24). Because vasculitis can affect any organ system, a complete history and physical examination and a detailed laboratory investigation are required.

Major coagulation defects and platelet disorders can be diagnosed through coagulation studies. Cutaneous vasculitis is diagnosed by skin biopsy. Systemic vasculitis is diagnosed by laboratory investigation. Treatment and disposition are based on the underlying diagnosis. For additional discussion, see chapters 141, "Rashes in Infants and Children" and 249, "Generalized Skin Disorders."

PYOGENIC GRANULOMA

A pyogenic granuloma is a benign proliferation of immature capillaries occurring at the site of minor skin trauma. The name is a misnomer because it is neither an infection nor a granuloma. It most commonly occurs in children, young adults, and pregnant women. In pregnant women, it is called granuloma gravidarum. A pyogenic granuloma initially presents as a bright red, shiny papule with a surrounding thin collarette of hyperkeratosis (Figure 253-25). It may be ulcerated and tends to bleed profusely with minor injury. Later, the lesion reepithelializes and becomes a dull red to purple color. Although lesions can occur anywhere on the body, the extremities, especially hands, are the most common sites of involvement. If the lesion is bleeding profusely, obtain hemostasis with pressure or suturing. Refer for a biopsy of the lesion to exclude other disorders, especially an amelanotic melanoma (Table 253-12). Lesions do not resolve without specific treatment by laser therapy or electrodesiccation.