RASH, GENERAL
RASH, GENERAL: Excerpt from Differential Diagnosis in Primary Care
The
best way to recall the causes of a general rash while still
examining the patient is to think of the mnemonic DERMATITIS.
D—Deficiency diseases include pellagra, scurvy, and vitamin A
deficiency.
E—Endocrine diseases recall the acne and plethora of Cushing
disease, the pretibial myxedema of hyperthyroidism, and the necrobiosis
lipoidica diabeticorum of diabetes mellitus. Xanthoma diabeticorum should
also be mentioned. Carcinoid tumors may cause a general erythema and
cyanosis.
R—Reticuloendotheliosis suggests Niemann–Pick disease,
Hand–Schöller–Christian disease, and Gaucher disease, as well as
Letterer–Siwe disease.
M—Malignancies suggest the rash of leukemia, Hodgkin lymphoma,
and metastatic carcinoma. In addition, certain malignancies induce skin
conditions such as herpes zoster (lymphomas), dermatitis herpetiformis,
dermatomyositis (gastrointestinal [GI] malignancy), or acanthosis nigricans
(abdominal malignancy). Multiple small metastases to the skin may suggest a
rash. Neurofibromatosis is a cause of multiple skin fibromas.
A—Allergic and autoimmune diseases includes
angioneurotic edema, urticaria, allergic dermatitis, erythema nodosum and
multiforme, and other skin lesions of rheumatic fever, dermatomyositis,
scleroderma, lupus erythematosus, periarteritis nodosa, and pemphigus.
Allergies to many foods and inhalants may cause a skin reaction.
Thrombocytopenia purpura and allergic purpura belong in this category.
T—Toxic disorders include drug eruptions from sulfa, penicillin,
and a host of other drugs. Serum sickness should be recalled here. Iodides,
boric acid, and many toxins in the environment may be responsible.
I—Infectious diseases are perhaps the largest category to
consider. They are best classified by the size of the organism working from
the smallest on up.
-
Viruses include the exanthema of measles, infectious
mononucleosis, rubella, smallpox, chickenpox, human immunodeficiency virus
(HIV), herpes zoster, viral hepatitis, and various Coxsackie and
echoviruses.
-
Rickettsiae include Rocky Mountain spotted fever and typhus.
-
Bacteria include typhoid, meningococcemia, miliary tuberculosis
(usually a focal lesion), Haverhill fever, brucellosis, leprosy, and
subacute bacterial endocarditis (SBE).
-
Spirochetes include syphilis, which may present any form of a
rash, but the lesions are usually small, indurated macules on the trunk,
palm, and, to a lesser degree, the extremities. Rat-bite fever and Borrelia recurrentis may also
cause a rash.
-
Parasites suggest New World leishmaniasis, hookworm,
toxoplasmosis, and trichinosis.
-
Fungi suggest histoplasmosis, which is more likely to produce a
general rash than coccidiodomycosis, blastomycosis, and spirotrichosis,
although all are associated on occasion with rash. Tinea versicolor is also
responsible for a diffuse rash, but most of the other fungi cause a local
rash.
T—Trauma suggests sunburn and other types of burns, such as
radiation.
I—Idiopathic disorders account for a number of diseases. In this
category one should remember psoriasis, lichen planus, epidermolysis
bullosum, ichthyosis, porphyria, neurodermatitis or eczema, the adenoma
sebaceum of tuberous sclerosis, and keratosis pilaris. Pityriasis rosea may
be due to a virus, but this is not established yet.
S—Sweat gland and sebaceous gland disorders include
miliaria (prickly heat) of the sweat glands and milia, folliculitis, and
carbuncles and furuncles involving the base of the hair follicle and
sebaceous glands. Acne rosacea and acne vulgaris can also be recalled here.
The diagnosis of a rash depends on a good history and a description of
the type of rash and its distribution.
Description (only the most typical are listed).
-
Macular rash. Typhoid, syphilis, pityriasis rosea, variola (in
early stages), rubella (first stages), and tinea versicolor fall into this
group.
-
Papular rash. Measles, German measles, HIV, miliaria, scabies,
drug eruptions, lichen planus, urticaria papulosa, warts, lupus
erythematosus, erythema multiforme, rat-bite fever, and infectious
mononucleosis generally present this way. Rocky Mountain spotted fever may
have a maculopapular rash prior to the purpuric rash. Reticuloendotheliosis
may also present this way.
-
Purpural rash. Meningococcemia, thrombocytopenic purpura from
any cause, Henoch–Schönlein purpura, Letterer–Siwe disease,
trichinosis, leukemia, SBE, and Rocky Mountain spotted fever and other
rickettsiae are in this category.
-
Vesicles. Contact or allergic dermatitis, miliaria, eczema,
variola and varicella, dermatophytosis, tinea circinata, herpes zoster,
poison ivy, scabies (one stage), and some drug allergies present this way.
Impetigo may start as a vesicle but usually quickly becomes bullous.
-
Bullae. Pemphigus, impetigo contagiosa, hereditary syphilis,
herpes zoster, dermatitis herpetiformis, and epidermolysis bullosa are
considered here.
-
Scales. Psoriasis, parapsoriasis, and lichen planus are the most
typical causes of this lesion, but most dermatoses may get to this stage
after chronic itching. Scarlet fever has a definite desquamative phase, and
pityriasis rosea will demonstrate scaling on scratching. Tinea versicolor,
the dermatophytoses, and exfoliative dermatitis must be considered here.
-
Pustules. Furunculosis and impetigo are the most typical types
of this lesion but they are usually focal rashes. Smallpox (variola) will
demonstrate pustules in the late stages, and chickenpox may do the same. It
is unusual for pustular lesions to be generalized.
-
Nodules. Erythema nodosum, erythema induratum, and
Weber–Christian disease fall into this category.
Distribution.
-
Trunk. Pityriasis rosea, drug eruptions, herpes zoster,
dermatitis herpetiformis, chickenpox, seborrheic dermatitis, and tinea
versicolor occur typically on the trunk.
-
Extremities. Smallpox and Rocky Mountain spotted fever often
begin on the extremities and work centripetally.
-
Palms of the hands. Four conditions typically occur here: Rocky
Mountain spotted fever, penicillin allergy, syphilis, and erythema
multiforme. Contact dermatitis, keratoderma, climacterium, warts,
keratoderma palmaris, dyshidrosis, and psoriasis may also occur here.
-
Feet. Tinea pedis, warts, purpuras, psoriasis, keratoderma
plantaris, syphilis, penicillin allergy, Rocky Mountain spotted fever,
acrodynia, varicose ulcers, diabetic ulcers, and ischemic ulcers may occur
here more often than elsewhere. Contact dermatitis from leather is important
to consider here.
-
Face. Acne vulgaris and rosacea, impetigo, seborrheic
dermatitis, milia, lupus erythematosus, lupus vulgaris, basal cell and
squamous cell carcinomas, eczema, contact dermatitis, and erythema
multiforme have a predilection for the face.
-
Groins and thighs. Scabies, pediculosis, intertrigo, tinea
cruris, moniliasis, and Weber–Christian disease occur here.
-
Antecubital and popliteal spaces. Eczema occurs here.
-
Extensor surfaces of elbow and knees. Psoriasis and
epidermolysis bullosa should be considered.
-
Shins. Erythema nodosum occurs here.
The description and distribution of all the dermatologic conditions
would take volumes. Only the most common or important ones have been
considered here.
Approach to the Diagnosis
Any condition with pus should be cultured. If a fungus is suspected, a
Wood’s lamp examination and a fresh potassium hydroxide (KOH) preparation
should be done. Skin biopsy is useful and is necessary in some cases. A
dermatologist should be consulted if there is any question about a
malignancy, if the condition persists, or if the symptoms are systemic. It
is foolish to persist in treatment without a definitive diagnosis for more
than 2 or 3 weeks when one may be dealing with something serious.
Other Useful Tests
-
Complete blood count (CBC) (chronic infectious disease)
-
Sedimentation rate (infectious disease)
-
Chemistry panel (collagen disease)
-
Platelet count (thrombocytopenia)
-
Blood cultures (SBE)
-
Venereal disease research laboratory (VDRL) test (secondary
syphilis)
-
Antinuclear antibody (ANA) analysis (collagen disease)
-
Allergy skin testing (allergic dermatitis)
-
Chest x-ray, barium enema, GI series, long bone survey (survey
for malignancy and various form of colitis)
-
HIV antibody titer (acquired immunodeficiency syndrome [AIDS])
-
Well–Felix reaction (Rickettsia disease)
-
Serology for Rocky Mountain spotted fever
-
Coagulation profile (disseminated intravascular coagulation
[DIC])
-
Serum immunoglobulin E (IgE) level (allergy)
-
Serum for viral studies (viral disease)
-
Streptozyme test (rheumatic fever)
-
Anticentromere antibody (scleroderma)
Pictures
Book Source Details
- Book Title: Differential Diagnosis in Primary Care
- Author(s): R. Douglas Collins MD, FACP
- Year of Publication: 2007
- Copyright Details: Differential Diagnosis in Primary Care, Copyright © 2007 Lippincott Williams & Wilkins.
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