The important thing is to establish there is no scale before using this algorithm. Remember that some scaly disorders lose their scale if treated with topical steroids and scaly diseases such as psoriasis lose their scale in moist flexures such as under the breasts and in the groin and axillae. In Australia it is also important to consider solar damage as a cause of a red non scaly rash especially on exposed areas such as face, forearms and lower legs, but most areas of significant sun damage are red and scaly
The more common disorders will be outlined first and representative photographs of them will be shown.
C Cellulitis Characterised by a hot, red nonscaly fixed tender area of skin which has arisen suddenly, typically on the lower legs over the shins or on the cheeks or around a recent injury to the skin. Lymphangitis ie a red line travelling towards the local lymph glands is a worrying sign!
For more information See DermNet
U Urticaria Raised itchy plaques in the skin that last a few hours and disappear only to reappear elsewhere. Individual lesions never last longer than 24 hours ecept for urticarial vasculitis where the lesions mat resolve but leave residual bruising at the site and papular urticaria secondary to an insect bite reaction where the mechanism causing the lesion is a delayed type cell mediated hypersensitivity reaction rather than the immediate IgE mediated histamine release from mast cells.
For more information See White Diseases of the Skin
L Lupus erythematosus, Light eruption (PMLE) Lues (syphillis)
These are rarer red non scaly rashes but should be considered in unusual eruptions
D Drugs You have to consider a drug reaction for virtually every red non scaly rash. Typically sudden onset, no fever, itch prominent and the rash is florid! Compare it with a virus infection where the onset can be just as fast and the rash just as florid but there is fever, little itch and the patient feels unwell. A drug reaction to an antibiotic given to a patient with a viral infection is always difficult to diagnose! Look for a viral enanthem.
For more information See White Diseases of the Skin
V Virus Viral infections can have a variety of morphologies but macular or maculopapular are the commonest and they are red and non scaly. The patient usually has a fever, some lymphadenopathy and feels ill. An enanthem is an associated finding often in the mouth. eg Koplick spots on the buccal mucosae in measles.
You can learn to diagnose viral exanthems by viewing this tutorial.
A Annular erythemas The annular erythemas look like urticaria but individual lesions last longer than 24 hours and often slowly join up with each other to form polycyclic rings. They can be easily misdiagnosed as a tinea fungal infection but they usually do not have a scale except sometimes the EAC or erythema annulare centrifugum variant.
For more information See DermNet NZ
E Erythema multiforme This condition looks like a drug eruption which it sometimes is! Again no fever or itch and few systemic features in the minor variant. The morphological feature you look for is the iris, bullseye or target lesion seen on the lower legs or palms of the hands and soles of the feet. Again the rash is red and non scaly, sudden onset lasting days, occassionally blistered in severe cases due to a drug and in the very severe cases will have involvement of the lips and conjunctival surfaces. In these circumstances it goes under the name of the Stevens-Johnson syndrome.
See White Diseases of the Skin or Dermnet NZ for further information.
V Vasculitis The early stages of true vasculitis give a red non scaly rash particularly on the lower legs or buttocks. It does not blanch with pressure and may be purpuric or small bruise like. Again drugs are the commonest cause but the potential range of causes is very great. The first thing to do is check the urine and see if there is any blood in it. If there is then you have a systemic vasculitis that can hit other organ systems including the joints, the gut , the lungs, heart and the brain. Wide ranging investigations are necessary to diagnose the cause.
See White's diseases of the Skin for an exhaustive discussion or DermNet for a more leisurely one.
E Erythema nodosum This red non scaly rash is also quite distinctive presenting as tender deeper nodules on the anterior shins or sometimes on the calves. The lesions may resolve with bruising before disappearing over a 2-3 week period. You have to consider a condition called erythema induratum when the lesions are mainly on the calves. Erythema nodosum is a form of panniculitis or inflammation of the deeper fat tissue. Again it can be a drug reaction but most cases are post streptococcal throat infection.
See Derm Net for more information.
Infiltrates can present as red non scaly rashes eg Generalised granuloma annulare, sarcoidosis, leukemic infiltrates, leprosy, leishmoniasis, mucinoses ie infiltrates of cells, substances or infectious agents (viral, bacterial, fungal and protozoal).
When you are considering the causes of the red non scaly rashes the underlying causes of cellulitis, drugs and viral infections are self explanatory but all the others have multiple potential causes because they are all reaction patterns in the skin, probably due to immune complex formation. As potential causes for each you should consider drugs, infections,collagen diseases eg lupus erythematosus, food colourants and additives and very rarely underlying malignancy!
So if the rash is red and non scaly then C U L ( later) at the Department of Veterans Affairs Evei (your girlfriend) (CUL DVA EVEI) where EVEI stands for Erythema multiforme, Vasculitis and Erythema nodosum and Infiltrates of cells or substances or infectious agents.
