R
Rash, General
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–Schüller–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. Dysplastic nevi syndrome is a hereditary condition associated with numerous moles of the scalp, trunk, and buttocks. Malignant transformation to melanomas is not uncommon.
A—Allergic and autoimmune diseases include 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.
Figures on pages 364, 365, 366, and 369 from Sauer GC. Manual of Skin Diseases, 4th ed. Philadelphia: JB Lippincott; 1980, with permission.
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 coccidioidomycosis, blastomycosis, and sporotrichosis, 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.
Rash, systemic causes.
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.
Rash, general. (From Hall BJ, Hall JC. Sauer’s Manual of Skin Diseases. 11th ed. Philadelphia: Wolters Kluwer; 2017.)
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.
Rash, general. (From Hall BJ, Hall JC. Sauer’s Manual of Skin Diseases. 11th ed. Philadelphia: Wolters Kluwer; 2017.)
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. Hand, foot, and mouth disease is associated with a vesicular rash of the hands, feet, and mouth and is caused by a coxsackie virus.
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.
Rash, general. (From Hall BJ, Hall JC. Sauer’s Manual of Skin Diseases. 11th ed. Philadelphia: Wolters Kluwer; 2017.)
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
The association of other symptoms and signs is extremely helpful in differential diagnosis. For example, a rash with bloody diarrhea might suggest Crohn disease or ulcerative
colitis. A rash with joint pain would suggest lupus or gonorrhea. A rash with lymphadenopathy should suggest syphilis or Kaposi sarcoma. Any condition with pus should be cultured. If a fungus is suspected, a Wood 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 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.
colitis. A rash with joint pain would suggest lupus or gonorrhea. A rash with lymphadenopathy should suggest syphilis or Kaposi sarcoma. Any condition with pus should be cultured. If a fungus is suspected, a Wood 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 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 forms of colitis)
HIV antibody titer (acquired immunodeficiency syndrome [AIDS])
Weil–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)
