You just ask yourself the following 3 questions.
1. Is the rash skin coloured or red AND is it scaly or non scaly?
2. Are there pustules or blisters?
3. Is it a funny shape, colour, texture or distribution?
The mnemonics are as follows. The red rashes are the commonest in white people.
1 PMs PET(AL) for red scaly diseases
2. CUL DVA EVIE for red non scaly diseases
3. II for pustular diseases
4. ICI for vesicular or Blistering diseases.
Diagnosis boils down to this -
What do I see?
What mnemonic will I use?
What are my likely differential diagnoses?
Where else will I examine or what tests will I do to arrive at the likely diagnosis?
What now is my preferred diagnosis?
Hence what is my treatment?
Diagnosis boils down to this -
What do I see?
What mnemonic will I use?
What are my likely differential diagnoses?
Where else will I examine or what tests will I do to arrive at the likely diagnosis?
What now is my preferred diagnosis?
Hence what is my treatment?
What do I see? This is obviously a red scaly lesion. Note there are two other smaller lesions near it.
What mnemonic will I use? The PMs PET mnemonic applies.
What are my likely differential diagnoses? Is it psoriasis, eczema or tinea?
Treated psoriasis can heal in the middle leaving a scaly outer edge. It is not broken or weeping on the surface for eczema. It has a peripheral scale for tinea so it could be a fungal infection.
Now what about the PM bit. Pityriasis rosea possible if this was the big herald patch early lesion. Pit rosea often has a trailing scale that points inward. Pit versicolor is less likely with the central clearing.
On balance this could be a tinea( ringworm) infection or the herald patch of pityriasis rosea.
Where else will I examine or what tests will I do to arrive at the likely diagnosis? The history would help but you should do some scrapings of the lesion's scaly edge for fungal microscopy and culture. You might also check the other usual sites for psoriasis.
Examination of this patient elsewhere showed the typical oval lesions following the lines of the ribs seen in pityriasis rosea.
What now is my preferred diagnosis? What we have been examining is the herald patch of Pityriasis Rosea.
Hence what is my treatment? View DermNet for more information on Pit rosea.
Case 2
What do I see? This rash is composed of multiple papules and nodules in the skin. They are smooth surfaced.
What mnemonic will I use? The mnemonic would be red non scaly rash ie CUL DVA EVIE
What are my likely differential diagnoses? The lesions are fixed . Not cellulitis or urticaria. Could be Lupus or Drug reaction Not vasculitis or Anular erythema. Not erythema multiforme, vasculitis or erythema nodosum (wrong distribution) Could be an infiltrate of cells, substances or organisms. eg neutrophils and Sweet's syndrome or lymphocytes and T or B cell lymphomas, or Mucin for a papular mucinosis or Amyloid for systemic amyloidosis
Where else will I examine or what tests will I do to arrive at the likely diagnosis? Check liver and spleen and lymph nodes, Ask about drugs especially new ones, Check bloods. Do a Biopsy. You almost certainly need a biopsy to diagnose possible skin infiltrates
What now is my preferred diagnosis? Skin Infiltrative disorder Biopsy showed myeloid leukaemic skin infiltrates! Blood count confirmed.
Case 3
This man was red all over and itchy.
What do I see? This is erythroderma with prominent skin scaling and possibly some crusts. Crusts can come from oozing serum or ruptured blisters.
What mnemonic will I use? The mnemonic would be red scaly rash ie PMsPET (AL) You could also later try ICI for vesicular or blistering diseases causing crusts.
What are my likely differential diagnoses? Psoriasis, Eczema, Generalised Mycosis fungoides (T cell lymphoma Sezary variant) The initial P of PMs can stand for Pharmaceutical and generalised drug reaction is possible. Another P would be Pityriasis rubra pilaris but it usually gives islands of sparing. s The little s stands for Solar, Scabies, Syphilis and Syndromes. Not solar, If scabies it would be the crusted type or severe scabies complicated by eczema from scratching, Syphilis does not look like this and Syndromes eg Dariers rarely goes erythrodermic unless complicated by herpes virus.
Where else will I examine or what tests will I do to arrive at the likely diagnosis? Good history for preceding psoriasis or eczema, Look at scalp for psoriasis, Any new drug or milder earlier drug reaction? Check typical areas for scabies. Check liver spleen and nodes for Sezary syndrome, Look for scabies with a dermatoscope. Swab for bacteria and viruses. Probably you are going to have to biopsy an erythrodermic case like this to exclude T cell lymphoma
What now is my preferred diagnosis? Clinically not clear. The dermatoscope showed multiple scabies burrows. This was crusted or Norwegian scabies with superimposed generalised infected eczema!
Case 4
What do I see?
What mnemonic will I use?
What are my likely differential diagnoses?
Where else will I examine or what tests will I do to arrive at the likely diagnosis?
What now is my preferred diagnosis?
Hence what is my treatment?
