DERMATOLOGY MINI:
THE 8 FOUNDATIONAL
PRINCIPLES
HANDBOOK
E. Paul Scheidegger, MD
Table of contents
Eight foundational principles in dermatology
Recognizing eczema
4
Identifying a one-sided lesion as a tumor or infection
11
Recognizing bilateral lesions as non-infectious
16
Diagnosing a transient rash as urticaria
20
Treating a scaling skin surface with a topical medication
23
Treating a smooth skin surface with systemic therapy
26
Diagnosing itchy versus non-itchy rashes
30
Looking for enanthema
35
Putting it all together
38
Appendix
Reference list
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43
2
EIGHT FOUNDATIONAL
PRINCIPLES IN
DERMATOLOGY
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Recognizing eczema
The most common dermatological condition that you will encounter in daily
practice is eczema. In this Medmastery lesson, you will learn how to recognize
and treat patients with this condition.
So, what exactly is eczema?
Eczema (or dermatitis) represents a group of non-infectious conditions in which
the skin becomes inflamed, dry, and scaly.
Clinically, eczema can be diagnosed according to the four following criteria:
1.
Itchiness
2.
Red color (also called erythema)
3.
Blister formation
4.
Scaling
Typical clinical examples
Take a look at the two images of eczema shown below. Usually, a rash caused by
eczema exhibits a reddish, rough, and scaling or blistering surface.
However, it is important to know that on non-white skin, this red color can be
more subtle. In patients with brown or black skin, the rash caused by eczema
tends to look darker brown, purple, or ashen grey in color.
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In the absence of characteristic redness, other symptoms may help physicians
confirm the diagnosis:
• Skin swelling
• Warmth
• Scaling
• Itching
Eczema in darker skin
Unique forms of eczema may also be observed in those with darker skin. For
example, African Americans more commonly develop small bumps on their legs,
arms, or torso. These bumps may develop around hair follicles and resemble
goosebumps. This is known as follicular accentuation.
It is important to be aware of these differences when assessing your patients.
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Histology
In each case, taking a skin biopsy from a patient with suspected eczema for
histological analysis can help confirm your diagnosis.
Take a look at the illustration of the hematoxylin and eosin-stained histological
section of skin shown below. The skin is composed of two main layers: the
epidermis and the dermis. In patients with eczema, inflammation causes damage
to the epidermis, resulting in a characteristic spongiotic tissue reaction pattern.
With this spongiotic tissue reaction, the epidermis appears to be full of bubbles,
and this explains the rough surface or presence of small blisters that can be
observed upon closer clinical inspection of patients with eczema. It is this
spongey surface appearance that dermatologists look for to support the
diagnosis of eczema.
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Distribution
The distribution of the patient’s rash can also provide important clues
for diagnosis. If you look closely, you will find a bilateral and more or less
symmetrical distribution of the red, scaling, and itchy bumps in most cases of
eczema.
The severity might be different on the left and right sides of the body, but this is
still considered to be a symmetrical pattern. Therefore, one-sided (or isolated)
rashes are typically not eczema.
Eczema also comes and goes over several days or weeks, and it is typically a
non-migratory condition.
Main causes
There are many causes of eczema, but the main cause is underlying inflammation
which is induced by one of three factors:
1.
Allergens
2.
Genetics
3.
Environmental factors
Next, let’s go over the two main causes of eczema:
1.
Atopic dermatitis
2.
Exsiccation dermatosis
Atopic dermatitis
The most common cause of eczema is atopic dermatitis, which is an inherited
chronic inflammatory skin condition. It results in itchy, red, swollen, and cracked
skin. Clear fluid may also leak from the affected areas.
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Exsiccation dermatosis
Exsiccation dermatosis is another common cause of eczema. This occurs
after excessive exposure to water and can develop when you wash your hands
regularly or shower too often.
Therefore, it is of utmost importance to regularly apply a moisturizer after
washing and showering.
Helpful tips
Eczema may look similar to other skin conditions, but there are some important
tips and tricks that can help you recognize and diagnose patients with eczema
without needing to refer them to a dermatologist. Let’s go over three.
1.
Eczema is the most common condition
One key thing to remember is that eczema is the most common skin
condition in ambulatory care, so if the patient’s history is lacking or noncontributory, or the images are poor, then assume it is eczema until proven
otherwise.
2.
Eczema is itchy
Itch is a hallmark of eczema, so if a rash diagnosed as eczema does not
itch, then you must consider a different diagnosis.
3.
Eczema does not cause a rash in the mouth
Eczema is typically not seen together with a rash in the mouth (known as
enanthema). So, if your patient presents with both a rash on their skin and
enanthema, then you must consider a different diagnosis.
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Eczema versus urticaria
Urticaria or hives is a common condition that is often confused with eczema.
Both conditions cause the skin to appear red, are symmetrical in distribution,
and are very itchy.
However, there are two key differences that can help you distinguish between
urticaria and eczema:
1.
Urticaria is a migratory skin condition so it moves around within 6–12 hours,
whereas eczema is a more stationary condition.
2.
Urticaria has a non-scaling, smooth surface, whereas a scaling or rough
surface is a characteristic sign of eczema that is never found in patients
with urticaria.
Treatment
Once you have reached a diagnosis of eczema, the next step is, of course,
treatment! The most effective treatment of eczema is the use of topical steroids
(1–2 times daily).
You should also advise your patients to take the following precautions:
• Stop any prior treatments and care products because they can be sources of
irritation or contact allergies
• Reduce contact with water
• Use a fragrance-free moisturizer without urea, since urea and fragrances can
potentially cause stinging or skin irritation
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So, there you have it! Keeping all of these important points in mind will help you
recognize and treat eczema in the clinic.
And remember, eczema is the most common skin condition, so if your patient
has a rash that you can’t identify, administer a trial of topical steroids twice daily
for 5 days. Most skin conditions should improve or even disappear with this
course of action. If not, then call the dermatologist!
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Identifying a one-sided lesion as a tumor or
infection
Being able to recognize a tumor or infection is the most important skill in
dermatology because these are urgent dermatological conditions. In this lesson,
you will learn that a one-sided or solitary lesion may indicate a tumor or infection,
and we will review some of the most common causes of these pathologies.
Below is an image of an epidermal cyst, which is a benign tumor, and an image
of a common fungal infection. Both should be addressed with high priority, but
they can sometimes look very similar to other less urgent skin conditions. Let’s
go over a few tips that will help you to differentiate.
How to differentiate tumors and infections from less urgent
diagnoses
Let’s cover two important things to consider when you are trying to distinguish
between tumors, infections, and less urgent diagnoses:
1.
Check the other side
2.
Notice the distribution
Check the other side
The key to arriving at the correct diagnosis is to assess the other (i.e.,
contralateral) side of your patient to confirm that the skin condition is actually
one-sided, which would indicate a tumor or infection. The patient may not have
exposed the other side when preparing for the exam, so you may need to help
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them to do so. They may even be hesitant to undress further because they don’t
see the need, but it is important to be persistent because examining both sides
will help you to determine the urgency of the condition.
If a lesion turns out to be bilateral (i.e., found on both sides of the body), then
you have to consider non-infectious or non-tumorous skin conditions, such as
inflammatory skin disorders.
Notice the distribution
The distribution is also important. When you see a solitary distribution where
only one part of the body is affected, it likely indicates the presence of a tumor or
infection, which requires immediate medical attention.
How to recognize common tumors and infections
Next, let’s learn how to recognize six of the most common tumors and infections:
3.
Melanoma
4.
Basal cell carcinoma
5.
Impetigo
6. Tinea
7.
Lyme disease
8.
Herpes simplex
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Melanoma
Melanoma is a potentially serious type of skin cancer characterized by the
uncontrolled growth of melanocytes, which are pigment-producing cells.
Melanoma typically has the following features:
• Brown or pigmented tumor
• Asymmetric in shape or form
• Often exhibits more than one color
• Typically shows some type of change or growth
Basal cell carcinoma
Basal cell carcinoma is the most common form of skin cancer. It arises from the
follicular or basal keratinocytes in the epidermis and is a locally invasive cancer.
Clinically, basal cell carcinoma has the following features:
• Solitary
• Expansile
• Often with elevated borders
• Typically ulcerated in the center
• Non-pigmented
Impetigo
Impetigo is a highly contagious superficial bacterial skin infection.
Patients with impetigo typically present with the
following signs:
• Pustules
• Honey-colored crusted erosions
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Tinea
Tinea is a superficial fungal infection of the skin that can affect any part of the
body. It is commonly referred to as ringworm.
Tinea presents with the following signs and symptoms:
• Characteristic ring-shaped lesions
• The lesions are often itchy
Lyme disease
Lyme disease is a tick-transmitted infection caused by
the Borrelia bacterial species.
Around 7 to 14 days after the infected tick bite, a red,
expanding patch of skin typically appears. This is the
most characteristic sign of Lyme disease and is known
as erythema migrans.
Herpes simplex
Lastly, herpes simplex is a common viral infection that
causes localized blistering. Herpes simplex is known
as cold sores or fever blisters, as recurrences are often
triggered by a febrile illness, such as a cold.
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Putting your skills into practice
Importantly, these common tumors and infections all show a one-sided or
solitary pattern. Let’s look at an example of how this type of distribution can help
you narrow down your diagnosis.
Let’s say that you see a patient who is complaining of lesions on their right leg.
Which diagnoses would you suspect if
What if you checked the contralateral
the lesions had a one-sided, localized
side and discovered that both legs
appearance?
were affected?
In this scenario, you may suggest a
In this scenario, eczema or psoriasis
diagnosis of an infectious condition,
is a more likely diagnosis because
such as tinea.
these non-infectious conditions
typically affect both sides of the body.
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Recognizing bilateral lesions as
non-infectious
Skin lesions with a bilateral distribution (meaning that they are found on both
sides of the body) are typically non-infectious in nature. In this lesson, you will
learn how using this principle can help narrow down your diagnosis, and we will
review the most common non-infectious conditions that cause bilateral skin
lesions.
Non-infectious, bilateral skin conditions
Let’s cover four common non-infectious, bilateral skin conditions:
1.
Eczema
2.
Urticaria
3.
Psoriasis
4.
Drug eruption
Eczema
Eczema is characterized by the following signs and symptoms:
• Red skin
• Scaling
• Itchy skin
While eczema can have several patterns, it typically has a bilateral and more or
less symmetrical distribution.
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Urticaria
Urticaria is another likely cause of bilateral lesions. It is characterized by one or
both of the following signs:
• Wheals (i.e., hives)
• Angioedema (i.e., swellings)
A hive is a superficial, skin-colored swelling, usually surrounded by redness, that
lasts anywhere from a few minutes to 24 hours. Hives are usually very itchy and
may cause a burning sensation.
Angioedema is deeper swelling within the skin or mucous membranes that can
be skin-colored or red. It typically resolves within 72 hours. Angioedema may be
itchy or painful but is often asymptomatic.
Urticaria typically has a bilateral and symmetrical distribution.
Psoriasis
Psoriasis is a chronic inflammatory skin condition characterized by the following
features:
• Red, scaly plaques
• Clearly defined borders
• Plaques can affect any part of the body
Psoriasis is particularly common in Caucasians but may affect people of any
race. There is also a genetic component as approximately one-third of patients
with psoriasis have a family member with this condition, which can help with
your diagnosis.
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Typically, the red, scaling, non-itchy lesions of psoriasis have a bilateral and
symmetrical distribution.
Drug eruption
A drug eruption is another common, non-infectious cause of bilateral lesions. A
drug eruption is an adverse reaction of the skin to a drug. Many drugs can trigger
this allergic reaction, but antibiotics are the most frequent cause.
The eruption may resemble exanthems (i.e., skin rashes) caused by viral and
bacterial infections. But an important tip to remember is that a skin rash in
adults is usually due to a drug, whereas a skin rash in children is typically caused
by viral or bacterial infections.
This type of rash can also closely resemble eczema, but scaling is not as
prominent as it is in patients with eczema. So, drug eruptions have the following
signs:
• Red skin
• Itchy skin
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Typically, the distribution of a drug eruption rash is bilateral and symmetrical.
So, if your patient has bilateral, itchy skin lesions with a more or less symmetrical
distribution, think non-infectious conditions, and always make sure to inspect
the entire body to ensure that you don‘t miss this important clue!
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Diagnosing a transient rash as urticaria
The most likely cause of a transient rash is urticaria. In this lesson, you will learn
strategies to recognize and treat this condition.
Signs and symptoms of urticaria
Patients with urticaria present with wheals (i.e., hives), angioedema (i.e.,
swellings), or both. Urticaria can affect any site of the body and tends to be
widely distributed.
Urticarial hives
Urticarial hives can be skin-toned or red in color and may be surrounded by a red
flare. The hives can be round or form giant patches. They are typically very itchy
and move around within 6 to 12 hours.
It is important to know that the redness surrounding hives in urticaria patients
with darker skin may be more subtle. In these patients, hives will appear as
swollen or raised bumps and will typically spread over a larger area of skin
compared with what is observed in patients with light skin.
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Angioedema
Angioedema is a swelling of the skin or mucus membrane.
Angioedema in the mouth
The presence of angioedema in the mouth indicates a more urgent dermatological
condition because the swelling may be obstructing the upper airway.
If a patient presents with angioedema in the mouth in the absence of hives,
this may indicate life-threatening conditions, such as hereditary or acquired
angioedema. These patients should immediately be given a systemic steroid,
antihistamine, and sometimes even adrenaline.
Acute versus chronic urticaria
Acute
Urticaria can be either acute or chronic. In patients with acute urticaria, the
hives are present for less than 6 weeks and typically resolve on their own.
Chronic
In those with chronic urticaria, hives are present for longer than 6 weeks. Chronic
urticaria is often referred to as idiopathic (meaning the exact cause is unknown),
but it is likely caused by an autoimmune or autoallergic mechanism.
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The most common form of chronic urticaria is urticaria factitia, which is
characterized by redness and swelling following a minor rub, stroke, or scratch
of the skin.
Treatment of urticaria
The main treatment of all forms of urticaria in adults and children is an oral
second-generation antihistamine. If the standard dose (e.g., 10 mg for loratadine
or any other non-sedating antihistamine) is not effective, the dose can be
increased up to fourfold (up to 40 mg of loratadine daily). Once the urticaria has
settled down, treatment should be stopped.
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22
Treating a scaling skin surface with a topical
medication
A scaling skin surface is often triggered by an epidermal insult and should be
treated with a topical medication. In this lesson, you will learn about the different
conditions that cause scaling and what treatments will be most effective.
Two common scaling skin conditions
Let’s discuss two common scaling skin conditions:
1.
Eczema
2.
Psoriasis
Eczema
Eczema is a common skin disease that exhibits scaling. In fact, scaling is one of
the criteria used to clinically diagnose this condition.
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Psoriasis
Psoriasis is a chronic inflammatory skin condition characterized by red and
scaly plaques that can affect any part of the body.
Differentiating between eczema and psoriasis
Eczema and psoriasis can look very similar as patients with these conditions
both exhibit a scaling surface. However, the presence of scaling plus itchiness
indicates that your patient likely has eczema. On the other hand, a scaling
surface that does not itch suggests that this patient likely has psoriasis.
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Treatment of eczema and psoriasis
Psoriasis and eczema are typically treated with emollients and moisturizers.
Emollients are used to soften the skin’s surface when it exhibits scaling by filling
in the gaps between skin cells. Moisturizers are used to add moisture to the skin.
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Treating a smooth skin surface with
systemic therapy
A non-scaling, smooth surface indicates systemic inflammation originating in
or around the vasculature of the skin (for example, in the dermis) and should be
treated with systemic therapy. In this lesson, we will review the most common
conditions that show a smooth, non-scaling surface, and you will learn what
treatments will be most effective.
Four common smooth skin conditions
Let’s cover four smooth, non-scaling skin conditions:
1.
Urticaria
2.
Erysipelas
3.
Viral or bacterial toxin exanthema
4.
Drug eruptions
Urticaria
Urticaria characterized by hives and swellings is a common skin condition that
is caused by internal inflammation. Urticaria is treated with an antihistamine
and / or steroid, and it is important to know that emollients and other topical
treatments will be ineffective.
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Erysipelas
Erysipelas is a potentially serious bacterial infection of the skin. It is also known
as St. Anthony’s fire due to the intense rash associated with it.
When erysipelas involves the face, the affected skin has a very sharp, raised
border and a smooth appearance.
Viral or bacterial toxin exanthema
A viral or bacterial toxin-related exanthema is a widespread rash accompanied
by systemic symptoms, such as fever, headache, and malaise. Exanthemas
during childhood are usually associated with viral infections.
Typically, a viral exanthema exhibits a non-scaling, smooth surface, although
there are notable exceptions to this clue.
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No treatment is required for most patients with non-specific exanthemas as
the condition is usually short-lived and resolves spontaneously. If necessary,
symptomatic treatment with acetaminophen to reduce fever in combination with
an oral antihistamine or emollient to relieve itch and dryness may be used.
Lyme disease
Lyme disease is an infection caused by the Borrelia species. Erythema migrans,
which is a smooth, expanding red patch of skin, is the most typical sign of Lyme
disease. Erythema migrans is mostly asymptomatic but can be itchy, sensitive,
or warm if touched.
Lyme disease is typically treated with systemic antibiotics.
Drug eruptions
Drug eruptions can appear as a variety of skin rashes. The most common type
of drug rash is the one shown in the image below: a red, non-scaling, intensively
itchy rash with a smooth surface.
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If your patient has a drug eruption, they should immediately stop taking all
drugs (except the vital or indispensable ones), and systemic treatment can be
administered.
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Diagnosing itchy versus non-itchy rashes
Itch is a particularly important symptom in dermatology and is defined as the
desire to scratch. The presence or absence of itch can help you to diagnose
patients who present with a rash. This is because an itchy rash is typically
caused by non-infectious conditions, whereas a non-itchy rash is most often
caused by a virus or bacterial toxin.
So, the first question that you should ask your patient is whether or not their rash
is itchy. This information will help you to narrow down your diagnosis.
Common causes of itchy rashes
Let’s review four of the most common causes of itchy rashes:
1.
Eczema
2.
Drug eruption
3.
Urticaria
4.
Chickenpox
Eczema
Eczema is the most frequent cause of an itchy rash. In addition to scaling, one
of the defining criteria used to clinically diagnose eczema is itchiness. So, if your
patient presents with a rash that is itchy, eczema is a likely cause!
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Drug eruption
A drug eruption, which is an adverse skin reaction to a drug, is another common
skin condition that produces a widespread itchy rash. Typically, the rash is nonmigratory.
You can usually distinguish between a drug eruption and other rashes because
the appearance of drug-induced rashes tends to coincide with starting a new
drug treatment. It will disappear over time once the patient stops taking the drug.
Urticaria
Urticaria characterized by hives and swellings may also be the cause of an itchy
rash. This condition can be distinguished from others because urticarial hives
usually move around within 6 to 12 hours.
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Chickenpox
Chickenpox is a notable exception to the principle that itchy rashes are caused
by non-viral conditions. Chickenpox is a highly contagious viral infection that
causes acute fever and a blistered itchy rash mainly in children.
Immunocompromised individuals are susceptible to the virus at all times, and
measures should be taken to prevent or modify the course of the disease if there
has been exposure to the virus.
It is important to know that the small red vesicles that are characteristic of
chickenpox may be more subtle in patients with darker skin. These can develop
into fluid-filled blisters and spread throughout the body.
Common causes of non-itchy rashes
Next, let’s cover three common causes of non-itchy rashes, which are typically
caused by a virus or bacterial toxin:
1.
Scarlet fever
2.
Infectious mononucleosis
3.
Viral pharyngitis
Scarlet fever
Scarlet fever is a bacterial illness that often presents as a non-itchy rash made
up of tiny pinkish-red spots that cover the entire body. It affects people who
have recently had sores that were caused by a toxin released by certain strains
of group A Streptococcus bacteria.
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It is important to know that in order to get scarlet fever, you must be susceptible
to the toxin produced by the Streptococcal bacteria. So, if two children of the
same family both have streptococcal infections but only one develops scarlet
fever, it is because that child was susceptible to the toxin and their sibling was
not.
Infectious mononucleosis
Infectious mononucleosis is a common infectious disease caused by the
Epstein-Barr virus. It is usually non-itchy and can be distinguished from other
rashes because it is typically faint. It can also cause mouth sores, and the
condition usually resolves after about a week.
Viral pharyngitis
Lastly, viral pharyngitis is a common infection that causes a sore throat. Typical
characteristics include a non-itchy rash accompanied by enanthema (or a rash
inside the mouth).
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Looking for enanthema
A rash in the mouth is referred to as enanthema, whereas a rash on the body is
called an exanthema. Whenever enanthema is found together with an exanthema,
you can be sure that the cause is viral or bacterial toxin-related.
In this lesson, you will learn how using this principle can help to narrow down
your diagnosis, and we will review the most common causes of enanthema
accompanied by exanthema.
Common causes of enanthema accompanied by exanthema
There are four common causes of enanthema accompanied by exanthema:
1.
Scarlet fever
2.
Chickenpox
3.
Infectious mononucleosis
4.
Viral pharyngitis
Scarlet fever
Scarlet fever can be recognized by a rash made up of tiny pinkish-red spots and
sores inside the mouth.
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Chickenpox
Chickenpox causes a blistering rash on the skin and blisters inside the mouth
mainly in children.
Infectious mononucleosis
Infectious mononucleosis causes a faint skin rash and sores inside the mouth.
Viral pharyngitis
Viral pharyngitis causes a non-itchy rash on the skin and a sore throat.
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Viral and bacterial toxin-related rashes can look very similar, and there aren’t
many differentiating symptoms. Therefore, if your patient has both enanthema
and exanthema, it is important to collect a swab sample to send to the lab for
diagnosis.
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Putting it all together
Now that you’ve mastered the eight foundational principles in dermatology, let’s
put all of this information together so you can use it in your daily practice. We’ll
review two algorithms that will help you to diagnose 80% of skin conditions.
Algorithm 1: Patients who present with a rash
The first algorithm will help you narrow down your differential diagnoses of
patients who present with a rash.
Rash
Is it migratory?
No
Yes
Is it accompanied by
enanthema?
Urticaria
Yes
Virus (e.g. SARS-CoV-2) or
bacteria (e.g. Streptococcus
in scarlet fever)
Eczema or
drug reaction
What does the
surface look like?
Rough
Eczema
No
Is it itchy?
No**
Yes
Psoriasis or
viral infection
What does the
surface look like?
Smooth
Rough
Smooth
Drug reaction
Psoriasis
Viral infection
Psoriasis typically does not itch; however, it can develop into eczematized psoriasis and become itchy
(but the itch is often not a predominant symptom).
**
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Is it migratory?
The first question you should ask is whether the rash is migratory. If it is, then
the most likely cause is urticaria. If the rash is not migratory, then you should
look in the patient’s mouth to determine whether the skin rash is accompanied
by enanthema.
Is it accompanied by enanthema?
If enanthema is present, then it is caused by either a virus, such as SARS-CoV-2,
or bacteria, such as Streptococcus in scarlet fever.
If there is no enanthema, then the next question you need to ask is whether the
patient’s rash is itchy.
Yes, it is itchy
If the rash is itchy, then it is either eczema or a drug reaction.
What does the surface look like?
To distinguish between these two conditions, ask yourself, What does the
surface look like? If it is rough, then eczema is the most likely diagnosis, but
if the surface is smooth, then your patient likely has a drug reaction.
No, it is not itchy
If their rash is not itchy, then it is most likely caused by psoriasis or a viral
infection.
Psoriasis typically does not itch, though it can become irritated and develop
eczematous changes. This form of eczematized psoriasis can subsequently
become itchy. However, based on the extent of skin ivolvement, the itch is often
not a predominant symptom of this condition.
What does the surface look like?
Again, ask yourself, What does the surface look like? A rough surface
indicates psoriasis, whereas a smooth surface suggests a viral infection.
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Algorithm 2: Patients who present with red lesions
The second algorithm will help you to diagnose patients who present with
red lesions.
Red lesion(s)
What is the distribution?
Isolated,
unilateral
Multiple,
bilateral
Are they migratory?
Infection (impetigo,
ringworm, herpes) or
tumor
Yes
No
Are they itchy?
Urticaria
No**
Yes
Eczema or
drug reaction
What does the
surface look like?
Psoriasis or
viral infection
What does the
surface look like?
Rough
Smooth
Rough
Smooth
Eczema
Drug reaction
Psoriasis
Viral infection
Psoriasis typically does not itch; however, it can develop into eczematized psoriasis and become itchy.
**
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What is the distribution?
If the lesion is isolated and unilateral, then you should think of an infection (e.g.,
impetigo, ringworm, or herpes) or a tumor. If there are multiple lesions with a
bilateral distribution, then the next question you should ask is whether they are
migratory.
Are they migratory?
If the lesions are migratory, then your patient has urticaria. If they are not, then
you need to ask, “Are they itchy?”
Yes, they are itchy
If the lesions are itchy, then eczema or a drug reaction are the most likely causes.
Similar to algorithm 1, you can distinguish between these two conditions based
on what the surface looks like.
What does the surface look like?
A rough surface indicates eczema, whereas a smooth surface indicates a
drug reaction.
No, they are not itchy
If the lesions are not itchy, then the patient most likely has psoriasis or a viral
infection.
What does the surface look like?
Again, these can be differentiated by asking, What does the surface look
like? A rough surface is characteristic of psoriasis, while a smooth surface
suggests a viral infection.
Feel free to print these algorithms out or download this handbook to your phone,
so next time you’re assessing your patient’s skin condition, you’ll have these
useful tools at your fingertips!
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APPENDIX
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Reference list
Croskerry, P. 2013. From mindless to mindful practice—cognitive bias and clinical
decision making. N Engl J Med. 368: 2445–2448. PMID: 23802513
Gerd, G. 2008. Gut Feelings: Short Cuts to Better Decision Making. 1st edition. New
York: Penguin Group.
Kahneman, D. 2012. Thinking, Fast and Slow. 1st edition. New York: Farrar, Straus and
Giroux.
Lowenstein, EJ. 2018. Dermatology and its unique diagnostic heuristics. J Am Acad
Dermatol. 78: 1239–1240. PMID: 29133237
Lowenstein, EJ and Sidlow, R. 2018. Cognitive and visual diagnostic errors in
dermatology: part 1. Br J Dermatol. 179: 1263–1269. PMID: 29962022
Lowenstein, EJ and Sidlow, R. 2018. Diagnostic heuristics in dermatology, part 2:
metacognition and other fixes. Br J Dermatol. 179: 1270–1276. PMID: 30171684
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