Dermatology - Bright Red Rashes

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Revision as of 12:20, 21 October 2011

Bright Red Rashes

• There are five primary players in bright red rashes:
  • Urticaria
  • Erythema multiforme
  • Morbilliform eruptions
  • Lupus erythematosus
  • Dermatomyositis

General tendencies

• In general, vascular reactions to insult can be described by color, topography, and time course:
  • Color: redness = erythema, results from excessive blood flow
  • Topography: raised lesions result from edmea
  • Time course: a reaction can be described as dynamic = evanescent
    • Note that evanescent means "soon passing out of sight or memory"
• These three classic vascular reactions (erythema, edema, and evanescent) best describe urticaria, erythema multiforme, and morbilliform reactions

Urticaria

• Urticaria is an allergic reaction that results in a bright red rash.
• Urticaria is colloquially known as "hives"
  • The offending antigen is usually from a virus, a food, or a drug
  • Physical factors can also induce urticaria (think "SPACE"): sun exposure, pressure, aquagenic, cold, exercise
• Pathogenesis of urticaria:
  • Induction of immune response results in a dilated (erythema), leaky (edema) vascular state that can be readily changed (evanescent)
  • Urticaria's EEE state is primarily driven by histamine acting on small dermal vessels
  • Purpura can result if immune complexes damage endothelium to the extent that RBCs escape into the tissue
    • Purpura generally lasts more than 24 hours at a single location
• The rash of urticaria is often described as being annular.

Erythema Multiforme

• Erythema multiforme is an allergic reaction that results in a bright red rash.
  • Note that both urticaria and EM are allergic reactions.
• Erythema multiforme is distinct from urticaria by its immune complexes and its apoptotic cytotoxic T cells.
• Erythema multiforme is classified as minor and major based on how severe the manifestation.
  • EM minor is usually caused by herpes simplex virus, especially when EM is recurrent.
  • EM major is usually caused by drugs
• EM Major has several named causes / syndromes: Stevens-Johnson syndrome and Toxic Epidermal Necrolysis
  • Both SJS and TEN are (usually) allergic reactions to drugs that result in necrolysis of keratinocytes of the lower epidermis.
  • Some consider TEN a more severe form or SJS.
• EM presentation:
  • Target lesions on palsm
  • Oral mucosal involvement
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  • http://im.unboundmedicine.com/medicine/ub/image?na=app:16010:ch18_8.bmp
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• Stevens-Johnson Syndrome images:
  • SJS presents with widespread "targetoid" lesions
    • Note that these targetoid lesions are different than the target lesions in classical EM presentation
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Target lesions versus Targetoid lesions

• Target lesions:
  • Have concentric circles, especially when there are three concentric circles
  • Have central duskiness or a central blister
  • Have a relatively wide pale circle in between
  • Have an outer, thin, moderately erythematous circle
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• Targetoid lesions:
  • Suggest zonality but don't have 3 distinct concentric circles
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Morbilliform Reactions

• Morbilliform reaction is through to be a T-cell mediated hypersensitivity to drugs or pathogens.
• Etiology can be drugs or pathogens
  • Many different drugs (including antibiotics) can cause morbilliform reactions
  • Many pathogens can cause morbilliform reactions; usually enterovirus or group A streptococcus
• One diagnosis the etiology by culturing the "company" kept by the rash
• Morbilliform reaction manifests same symptoms regardless of causative agent
• Morbilliform reaction is less evanescent than multifomre erythema and urticaria
• Morbilliform reaction is characterized by truncal predominance
  • Recall that urticaria could show up anywhere and multiform erythema usually involved the oral mucosa and palms of the hands
• Morbilliform is marked by its maculopapular rash
  • Recall that a macule is NOT raised but is discolored and that a papule IS raised but not necessarily discolored.
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Viral Exanthems

• Most viral exanthems manifest as morbilliform reactions (except for varicella).
  • Recall that an exanthem is a skin eruption secondary to systemic disease.
  • Recall that varicella is a viral infection with herpes.
• Recall the viral agents that cause the classic pediatric exanthems:
  • These all cause MORBILLIFORM reactions
  • Rubeola (Measles, paramyxovirus infection): cough, coryza, conjunctivitis, koplik spots
    • Rubeola is a systemic infection by paramyxovirus of the genus Morbillivirus
  • Rubella (German Measles, rubella virus infection): 3 day progression, progresses toward cephalocaudal poles
  • Roseola (Roseola Infantum, roseola virus infection): fever, followed with rash when "defervesce"
  • Mononucleosis: fever, fatigue, (f)pharyngitis, adenopathy, liver / spleen involvement
  • Fifth disease (Erythema infectiosum): slapped cheeks, fishnet erythema, recurrence
    • An example of "multiple stages" seen in many viral exanthems

• Viral exanthums are characterized by: "dew drop on rose petal" formation, umbilicated vesicles, and multiple stages:
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Lupus Erythematous

• Lupus erythematous is an autoimmine disease
• There are three types of lupus: systemic (SLE), discoid (DLE), and subacute cutaneous (SCLE)
  • Systemic and subacute cutaneous can be induced by drugs
• All three types of SLE are considered idiopathic.
  • A genetic predisposition has been demonstrated.
• SLE (systemic lupus erythematous) requires 4 of 11 ARA criteria be met.
• DLE (discoid lupus erythematous) is primarily cutaneous in manifestation.
• SCLE (subacute cutaneous lupus erythematous); subacute means it is not quite acute or chronic.
• Pathogenesis of lupus eyrthmatous is though to be UV radiation induced and involves formation of immune complexes'.

Systemic lupus erythematous

• Systemic lupus erythematous has 11 diagnostic criteria that can be divided into skin and mucus, systemic, and laboratory findings.
  • To diagnose SLE, you must "DUMP the SAC on the RAC"
• Skin and mucosal criteria (DUMP):
  • Discoid lupus
  • Ulcers (oropharyngela, usually painless)
  • Malar rash
  • Photosensitivity
• Systemic criteria (SAC):
  • Serositis (pleural, pericardial): inflammation of the serous tissues--things that line the lungs / heart (pleura, pericardium)
  • Arthritis
  • CNS (seizures, psychosis)
• Laboratory criteria (RAC)
  • Renal dysfunction (Urinary analysis, elevated 24-hour urine protein levels)
  • Antinuclear antibodies (or others like anti-dsDNA or anti-Smith)
  • CBC (Hematology)
• DUMP the SAC on the RAC (skin / mucosa, systemic, lab)

• Systemic lupus erythematous presents with a malar rash and photosensitivity
  • There is sometimes "spillover" to unexposed sites, too, with the photosensitivity.
• SLE can manifest scarring alopecia

Dermatomyositis

• Dermatomyositis is an inflammation of the skin and muscle.
  • Note that polymyositis is simply the inflammation of the muscle with no skin features.
• Like lupus erythematous, most dermatomyositis cases are idiopathic.
  • A small subset of dermatomyositis are drug-induced.
• There is a definite role of UV radition in inducing dermatomyositis
• Dermatomyositis is characterized by involvement of the complement systems membrane attack complex (MAC)

• Diagnostic criteria for dermatomyositis:
  • Not all 5 are required
  • Skin features (to differentiate it from polymyositis)
  • Proximal muscle weakness which is usually painless
  • Muscle enzyme abnormalities (identified with CPK and aldolase levels)
    • CPK: creatine phosphokinase; adds kinase to creatinin; MM isoform in skeletal muscle, MB isoform in cardiac muscle, BB in smooth muscle
  • EMG abnormalities
  • Muscle biopsy
  • (currently we use MRI to dx, too)

• Dermatomyositis presentation:
  • Heliotrope rash (upper eyelids)
  • Photosensitivity with spillover
  • Poikiloderma: see next section
  • Gottron's papules (area between knuckles is spared)
  • Periungual telangiectasias

• Heliotrope rash (upper eyelids):
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• Photosensitivity with spillover:
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• Poikiloderma: see next section
• Gottron's papules (area between knuckles is spared):
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• Periungual telangiectasias:
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Poikiloderma

• Poikiloderma is characterized by hyperpigmentation, hypopigmentation, telangiectasias, and / or atrophy.
• Poikiloderma is seen in conjunction with dermatomyositis, UV radiation damage, and ionizing radiation damage.
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Drug reactions

• Drug reactions can generate every possible different cutaneous pattern
• Rarely does clinical presentation afford enough information to dx drug-induced reaction
  • Usually requires additional information like lab values
• Some patterns caused by drug reactions are considered higher risk
  • These patterns have significant morbidity or have mortality associated with them
  • High risk patterns include: urticaria / anaphylaxis, erythema multiforme major (SJS, TEN), morbilliform reactions (with hypersensitive syndrome characteristics), and vasculitis
• All the rest of the patterns are relatively low risk for morbidity and mortality.

An algorithm for diagnosing drug-induced cutaneous reactions

• The process is, in general, a series of controlled challenges to the pt with the drug: challenge, dechallenge, rechallenge, exlusion
• First we challenge with the drug
  • An important aspect to the challenge is the time of drug administration
  • This should be informed by the literature and one's own experience with the drug
• Then we "dechallenge"
  • We watch for cessation of the drug reaction
  • Dechallenging is options, unless the drug is essential for the pt's life
  • Dechallenging will not result in cessation of recation if the reaction is irreversible
• Next we rechallenge
  • This repetition gives the highest level of certainty that the reaction is drug-induced
  • Rechallenging is optional
    • Rechallenge is not an option if the challenge resulted in a higher-risk reaction pattern (which would advise no rechallenge for safety reasons)
    • Rechallenge is not an options if there is an alternative therapy to the drug that causes a reaction (because we shouldn't give a drug we know causes an adverse reaction is there is still another potentially non-reactive drug available)
• Finally we exclude
  • If the dechallenge does not generate cessation or if the rechallenge does not cause the same reaction the we exclude drug-induced reactions from the ddx.