You have a rash and you want to know what it is and how to fix it.

 You have a rash and you want to know what it is and how to fix it. Well if we combine artificial intelligence with some background knowledge from the Australian Institute of Dermatology websites that should not be too difficult.

Take your mobile phone camera and photograph the rash yourself or get someone else to do it. Make sure you have good lighting. Take 3  photos. 1 An overall picture of the rash. 2. Then take a close up. Show the surface of the rash especially any scale or small fluid filled vesicles or blisters and 3. take several images if the rash looks different in different areas.

You then upload the images to your computer . Open an image in Chrome and then right click on your mouse to show Search this image with Google lens and see what comes up. Then provide more information about the rash. Is it red and scaly or red and non scaly? Are there pustules or fluid filled vesicles or blisters. See what options then come up. 

At this point go to the following websites from the Australian Institute of dermatology. 

www.practicaldermatology.blogspot.com   and www.dermoclinical.com  and look at images of the conditions that Google lens has suggested.

If you use Microsoft the other option is top use Copilot. Here click on the + sign at the left base of the Message area and upload all your images into Copilot and add some details of the rash distribution on the body and then see what it says before looking  at the AID websites above. 

Look at the video below for examples of how this can be used. New rash

Diagnosing your rash.

You an diagnose the rash by  What it looks like or alternatively by Where the rash is found on the body.

What the rash looks like.

Red and scaly - Scale is white material on the surface when you scratch it.

Red and No Scale 

Can be flat (macular)  or raised  (papular or nodular)

Pustules

- Yellow fluid filled small blisters

Vesicular or Blisters - Clear fluid filled small blisters

Rash is a Funny Shape, Colour Texture or Distribution on the body

Where is the rash on the body

Red Scaly Diseases

Diagnosing skin diseases is not difficult. You look at a rash and decide if it is red and scaly or red and non scaly. If it is red and scaly you use the mnemonic PMs PETAL (PET is Psoriasis, Eczema and Tinea, Annular Erythema and Lupus. The first P of PM is for Pityriasis rosea or Pityriasis versicolor, Pityriasis Rubra Pilaris, Pityriasis Lichenoides and the M is for Mycosis fungoides, a T cell lymphoma of the skin.) The only additional problem we have in Australia is the extent of our solar damage which can masquerade as a red scaly rash and even be non scaly. So add solar damage after the mnemonics for both the red scaly and non scaly rashes.
View GlobalSkinAtlas for Images
Click the arrow to start the video below then click the wheel at the base and reset quality to HD. View  on YouTube by clicking the link at the base or Full screen by clicking the outside box at the base.

Now we know that his pet cat is called PETAL. This helps us to remember Psoriasis, Eczema and Tinea but also the less common red scaly diseases of A for Annular erythemas and L for Lupus erythematosus and Lichen Planus.

In this group there are five conditions that are common. These are psoriasis, eczema, tinea , pityriasis rosea and pityriasis versicolor. Other less common conditions include mycosis fungoides, lupus erythematosus, parapsoriasis, lichen planus and several other pityriasis conditions such as pityriasis rubra pilaris and pityriasis lichenoides
The more common disorders will be outlined first and representative photographs of them will be shown.

Step 1 Once you have decided that a rash is red and scaly look to see if the scale is broken and if there are cracks in the surface with any oozing or weeping. If there are, then it is a form of eczema, probably discoid eczema, rather than psoriasis or one of the other red scaly disorders. If it is not, then Step 2 scratch it first of all and see the nature of the scale. If you get the silvery wax like scale of psoriasis you are home and hosed. If you do not, then Step 3 the first thing you should do before you even look elsewhere is to take some scrapings for fungal culture. You should do this before you treat any red scaly rash rather than afterwards. Pityriasis rosea you will diagnose because of the herald patch, oval shaped lesions and the distribution along the rib lines on the trunk and Pityriasis versicolor because the lesions will either be whiter than the surrounding tanned skin or pinker than the surrounding white skin, depending on whether it is summer or winter!

Psoriasis
This is a composite image of psoriasis.



For more information on psoriasis try this reference.
Additional Diagnostic Features In psoriasis he skin grows 8 to 10 times faster than normal so you get this thick build up of scale that is easily scraped off. The lesions are usually quite sharply defined, the colour is often a salmon pink colour, except in the more inflammatory irritated types of psoriasis where it can be much redder. You should look at the more typical areas where you would expect to see psoriasis such as the elbows, the knees, the scalp. Look at the nails and see if there is any evidence of pitting. Look under the flexures and the elbows or breasts or in the groin area or especially around the anus to see if there is the relatively smooth non scaly lesions that occur in these areas.
Psoriasis on the lower legs can have an eczematous look to it as well because of stasis features and underlying varicose veins because the patient may have rubbed and scratched the psoriasis. This should not put you off making the diagnosis.

Eczema Red and scaly but with small erosions or breaks in the skin surface, sometimes oozing and often secodarily infected with Staph aureus.



For more information on Eczema View this reference
Additional Diagnostic features Eczema is usually itchy. The small erosions or breaks in the skin surface are the crucial diagnostic feature as is the distribution on the front of the elbow and behind the knee. Contact eczema remains localised at unusual areas depending on what and where you have been applying something you are allergic to.

Tinea Red and scaly but with a spreading edge. Scrape this for microscopy and culture. There may be small pustules in the edge in rare cases. Treatment with topical steroids will reduce the redness and scale making diagnosis more difficult.



For more information on Tinea View this reference

Additional Diagnostic Features The slowly spreading scaly edge is a hallmark of the condition. Seldom itchy. Usually not symmetrical like psoriasis or eczema. Fungal infections from animals are usually more inflammed.



Pityriasis rosea Red and scaly but has the herald patch appearing first with it's peripheral scale , followed within the week by the other oval shaped, scaly lesions running along the rib lines. May involve axillae and groin but seldom further down the limbs. Trunkal rash predominantly. Guttate psoriasis is your main differential diagnosis.



For more information on Pityriasis rosea View this reference

Additional Diagnostic Features The peripheral scale is not found on every lesion. It is seldom seen on the face. The sun helps it to go more quickly. No other systemic symptoms despite it probably being a viral infection. Usually not itchy.

Pityriasis versicolor This red scaly disease has fine bran like scale elicited by scratching the surface. It is usually seen on the trunk or under the breasts. It presents as white spot disease in tanned individuals and a red scaly disease on white skin.



Additional Diagnostic Features Often a very light pink colour and easy to miss. Look especially on the upper back, axillae and under breasts.

For further information on Pityriasis versicolor
See this reference or view additional images in Globalskinatlas.

The M in PMs PET is for Mycosis fungoides. This is an old name for T cell lymphoma of the skin. It is quite rare but important to diagnose because an early lesion can look like psoriasis or low grade eczema. This can be seen in the composite image below.




Additional Diagnostic Features This is a clinical diagnosis early because the initial biopsy may not be diagnostic. Fixed or slow growing plaque, sharp edges sometimes in bizarre shapes. Itchy later when they thicken.

For further information View this reference or see other images in Globalskin Atlas

We have mentioned that the PMs PET is called PETAL. The AL is to remind you of some other red scaly diseases including the Annular erythema called EAC or erythema annulare centrifugum and the L to remind you of Lupus erythematosus and Lichen planus.
EAC will remind you of a fungal tinea infection but it has a trailing or inward looking scale rather than at the edge as in a fungus and the lesions grow quickly and often merge together.
See this example from Globalskin Atlas

The L for lupus erythematosus refers to the discoid type which is usually seen on the face or back. On the face you will mistake it for sun induced skin cancer but if you freeze it then it will just come back around the frozen area! The scale is throughout the lesion, and is very adherent sometimes going into the hair follicles and giving a carpet tack appearance underneath when you try to lift it off!
See these examples from Globalskin Atlas or for more information on Discoid Lupus View this reference.



Other P diagnoses There are several other rarer skin diagnoses that are red and scaly and begin with Pityriasis. These include pityriasis rubra pilaris, pityriasis lichenoides and pityriasis alba. A composite of these conditions is shown below and there are links to global skin atlas and dermnet for further information.

Red Non Scaly Rashes

If it is red but not scaly consider Cellulitis, Urticaria, Drug reaction, Viral exanthem or Annular erythema. The mnemonic is C U L at the Department of Veterans Affairs Evie (your girlfriend) (CUL DVA EVIE) where EVIE stands for Erythema multiforme, Vasculitis , Infiltrates and Erythema nodosum. 
View GlobalSkinAtlas for Images
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.

Click the arrow to start the video below then click the wheel at the base and reset quality to HD. View  on YouTube by clicking the link at the base or Full screen by clicking the outside box at the base.




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     or images at GlobalSkinAtlas


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 GlobalSkinAtlas


L Lupus, Light eruptions, Lues  Some forms of Lupus erythematosus are not scaly eg Systemic lupus, Tumid Lupus , Lupus panniculitis and some cases of Subacute Lupus. These rashes are usually maximal on sun exposed areas as is Polymorphous light eruption. The latter occurs with unusual sun exposure particularly to people on holiday in sunny locations they are not used to. The lesions are usually itchy papules or plaques.

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  Dermnet




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.

GlobalSkinAtlas for images 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.


GlobalSkinAtlas Images or DermNet for more details

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. Images in Global Skin Atlas

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 at the Department of Veterans Affairs EVIE (your girlfriend) (CUL DVA EVIE) where EVIE stands for Erythema multiforme, Vasculitis , Infiltrates of cells or substances or infectious agents and Erythema Nodosum

Pustular Diseases

If there are Pustules then the mnemonic is II
(aye aye) Infective( viral, bacterial, fungal) or Inflammatory eg psoriasis or a pustular drug reaction. Common causes include Staph folliculitis , modified fungal infection or if the vesicles are grouped herpes simplex. Pustules on the face are Acne, Rosacea, Staph folliculitis or H Simplex if grouped.

Click the arrow to start the video below then click the wheel at the base and reset quality to HD. View  on YouTube by clicking the link at the base or Full screen by clicking the outside box at the base.

When we see pustules we have a tendency to think infection and often limit ourselves to only bacterial infections at that. Remember pustules can occur with fungal and viral infections as well and never forget that some pustules are not due to infection but to infiltration of the skin by neutrophils in Inflammatory skin diseases such as psoriasis and drug eruptions (localised AGEP and halogenodermas) and Sweet's syndrome. 

There are also a few other very rare inflammatory disorders such as acrodermatitis enteropathica (zinc deficiency) and the glucagonoma syndrome from underlying pancreatic malignancy that can have pustules at the advancing edge of the lesion and thereby simulate a fungal infection. 

Other rarer inflammatory conditions with pustules in an advancing edge are subcorneal pustular dermatosis and IgA pemphigus, erosive pustular dermatosis and folliculitis decalvans of the scalp. Some pustules are due to eosinophils such as those in neonates with Toxic erythema of the newborn and neutrophils in transient neonatal pustulosis of the newborn. 

Infantile acropustulosis of the feet is also non infectious and probably a reaction to previous scabies. Behcet's can give inflammatory pustules at sites of injury (pathergy) and you can see them in Bowel associated dermatitis -arthritis syndrome. 

Eosinophilic pustular folliculitis is seen in HIV cases. 

Pustules can also bee seen in Septic vasculitis. So remember Inflammatory as well as Infectious!

The images below include variants of pustular psoriasis, both localised and generalised and infected pompholyx eczema.

Vesicular Diseases

Vesicles are small clear fluid filled deep seated lesions in the epidermis. They are a feature of eczema/ dermatitis when acute in onset but can also be seen in delayed type hypersensitivity reactions such as a reaction to tinea on the soles of the feet. They are usually itchy and can subsequently become pustular from secondary bacterial infection. If you have pustules enquire if they were clear fluid filled lesions initially. If they were pustules initially then consider pustular psoriasis.  

The development of herpes simplex superimposed on a background atopic eczema is always a diagnostic problem but look for a sudden painful deterioration in the condition particularly with painful lesions appearing around the eyes.

So the mnemonic for vesicles is the same as for Blisters ie ICI (Infective , Contact dermatitis and Inflammatory and Immunological.)

Infective vesicles - Viral - herpes simplex  and Zoster, Chickenpox, (Varicella) , hand foot and mouth, Covid, Orf, 

                               Bacterial - Bullous impetigo, Blistering distal dactylitis

                               Fungal -  Vesicular tinea soles of feet

                               Syphilis - Malignant type in HIV

                               Rickettsia - Rickettsial pox

The other causes of Contact, Inflammatory and Immunological vesicles are best looked at in the Blistering section.

Contact - Allergic and irritant dermatitis, Atopic and Discoid eczemas , Pompholyx eczema , 

Inflammatory - Drugs, PCT , Miliaria, Arthropod bite particularly fire ants, Jellyfish stings , Hailey Hailey and Dariers 

Immunological - Bullous pemphigoid, Dermatitis herpetiformis, Linear IgA disease, EB Acquisita, Rarely pemphigus (usually crusts), Bullous lupus erythematosus

Rare Genetic - Kindler Syndrome - trauma-induced skin blistering (mostly on the hands and feet) starting in infancy, skin photosensitivity that improves after childhood, and progressive poikiloderma (a combination of skin thinning, color changes, and tiny blood vessels) Consider inherited EB variants in neonatal vesicles and Incontinentia pigmenti .



View this discussion of dermatitis in DermNet NZ

Blisters

If there are Blisters The mnemonic is ICI(Imperial Chemical Industries) Infective  Contact dermatitis  Inflammatory including Immunological,

Infective causes of blisters are usually staph toxin in origin and go under the name of bullous impetigo. However if the lesions are in a linear distribution but painful and limited to skin dermatomes then consider Herpes zoster or shingles. The Bullous insect bite reaction occurs on the lower legs usually from sand fly bites and the blister is tense and intact.

Inflammatory causes can include drugs but remember Immunological causes in the elderly particularly bullous pemphigoid. Contact dermatitis usually gives smaller vesicles rather than blisters but individual vesicles can join up into blisters. Watch for hair dye allergies around the posterior neck and scalp or consider a plant contact dermatitis if the blisters or vesicles are in a linear streaky distribution on exposed surfaces where the patient has brushed up against an offending bush or tree.

Blistering Inflammatory  drug eruptions are rare but can be seen with the anti epileptic drugs. They are usually explosive in onset and there may be mucosal involvement. 

Metabolic disorders rarely give rise to skin blisters but a notable exception is seen in porphyria cutanea tarda PCT. These blisters are usually seen on the backs of the hands or feet in sun exposed areas. The blisters are firm and take time to burst. They surrounding skin is not inflamed. An immunological bullous disease that can look very similar is epidermolysis bullosa acquisita, usually seen at sites of trauma.

Click the arrow to start the video below then click the wheel at the base and reset quality to HD. View  on YouTube by clicking the link at the base or Full screen by clicking the outside box at the base.

A more advanced overview of nearly all possible causes of blisters is shown below. A GP would rarely need to refer to it!

Blisters on the trunk include those on the chest,back and abdomen.  On these areas blisters are usually due to Herpes Zoster(unilateral and painful) bullous staph infection, bullous pemphigoid, plant contact dermatitis and drugs causing toxic epidermal necrolysis. Pemphigus blisters are fragile and soon form crusts and erosions. Rarer immunobullous diseases such as dermatitis herpetiformis and linear IgA disease will cause blisters in these areas. Fixed drug eruption may cause localised blistering and leave post inflammatory pigmentation when they heal.

Management Culture for bacteria and viruses, do a Tzanck smear, do a gram stain and biopsy and immunofluorescence if you consider an immunobullous disease is likely.

Herpes Zoster

Bullous pemphigoid

Plant contact

SIGN DIP MEN Overview of Blisters

S-Squamous Bullous Dariers disease, Bullous Lupus erythematosus

I-Infective Impetigo, Staph scalded skin syndrome, Herpes zoster, Bullous tinea, Parvovirus B19, Staph infected varicella, Bullous orf, Pseudomonas septicemia, Hemorrhagic bullae with Vibrio vulnificus, Mucor infection in immunosupressed, Blistering dactylitis

G-Granulomatous

N-Neoplastic Paraneoplastic pemphigus, Bullous mastocytosis, 

D-Drugs Toxic epidermal necrolysis, Fixed drug eruption, Numerous drugs causing the immunobullous diseases, Pseudoporphyria, Barbiturate coma,

I-Immunological Plant contact dermatitis, Phytophoto dermatitis, Erythema multiforme, Bullous pemphigoid, Pemphigus, Dermatitis herpetiformis, Linear igA disease, Chronic bullous dermatosis of childhood, Bullous lupus, Mucosal Pemphigoid, Epidermolysis bullosa acquisita, Herpes Gestationis, Lichen sclerosus , Bullous morphea, Bullous necrotising vasculitis,

P-Physical Friction blister, Burns, Insect bite reaction, Bullous scabies, Lymphedema, Puva blisters, Tanning bed Pseudoporphyria, Polymorphous light eruption, Edema blisters of the leg, Sucking blisters in neonates,  Epidermolysis bullosa,

M-Metabolic Porphyria cutanea tarda, Diabetes mellitus, Amyloidosis, Blisters of hemodialysis, Mastocytosis,

E-Endocrine Hypothyroidism,

N-Nutritional Pellagra, Acquired zinc deficiency, Acrodermatitis enteropathica,

Others Pompholyx eczema palms and soles, Congenital syphilis, Kindler syndrome, Neonatal purpura fulminans, Incontinentia pigmenti, Bullous ichthyosiform erythroderma

Hemorrhagic Blisters pemphigus, herpes zoster, leukemia, lichen sclerosus, Mucosal pemphigoid

Erosions Pemphigus, Hailey Hailey, Eczema herpeticum

Sheets of skin Staph scalded skin syndrome, Toxic epidermal necrolysis