Introduction to Clinical Dermatology

Introduction to Clinical Dermatology
We’ll start with the basic structure of the skin, and as we probably know, the skin consists of two layers: dermis and epidermis.
The epidermis has only one type of structures which are cells -no blood vessels, no lymphatics-, and the majority of those cells (about 85% of those cells) are called “keratinocytes”. The rest are called melanocytes, merkel cells, and langerhans cells.
The cells in the epidermis are arranged into 4 layers: * Basal layer: it is where we have mitosis, and then the cells will migrate to the layers above. * Prickle cell layer (spinous or squamous). * Granular layer. * Horney layer: it is the uppermost layer in the skin, and it is the layer that we see and touch on the surface of the skin, and it is composed of dead cells that had lost their nuclei. As you can see in the picture that the basophilic structures (the nuclei) are not present in this layer. Although the horney layer has dead cells, it is an important layer in the epidermis because it forms a physical barrier line to protect the internal environment. So problems and diseases affecting the horney layer will impair this protecting function leading to infections, allergies…

This is how the skin looks under the microscope. The bulk of the skin is dermis; 9/10th of the skin is dermis, and the bulk of dermis consists of collagen (mostly type 1 collagen). The blue things are the nuclei, and the horney layer is devoid of nuclei. And this is the normal basket-weave appearance of the skin.
Epidermal cells: * Keratinocytes: the majority. * Melanocytes: they are the color-producing cells in the epidermis that produce melanin which is then transferred to keratinocytes. Melanin absorbs UV light and inactivates it, otherwise we have a risk of having cancer. So western communities that have a white skin color (low activity of melanocytes) are more prone to have skin cancers, and the most common type of cancer in the western community is skin cancer; in particular the basal cell carcinoma. * Langerhans cells: they are the macrophages of the skin, and the predominant antigen-presenting cells in epidermis and dermis. And as we know, macrophages have different names in different tissues; in the liver they are called kupffer cells, and in the brain they are called microglial cells. Their function is to take the antigens, process them, and then present them to T lymphocytes, and then they go to the lymph nodes where their action starts. * Merkel cells: they are modified transducers for fine touch.

The dermis:
The dermis consists of several components: * Fibers (collagen and elastin). * Ground substance (glycosaminoglycans) that hydrates the skin. * Several types of cells: Fibroblasts (they produce collagen and elastin), Lymphocytes, Macro, Mast cells… * And it has appendages; Glands like sebaceous glands that produce sebum that moisturizes the skin, Apocrine and Eccrine glands that produce sweat that has a function in the thermoregulation of the body; Hair follicles, and Nails. * Also we have supportive structures; nerves, lymphatics, vasculature, smooth muscles. So if a lesion bleeds, then we know that the pathology is in the dermis.

Now, how do we approach patients with a skin disease? * Don’t be shy to introduce yourself as a medical student! Only few of your previous colleagues in the school could get into the medical school, so be proud to say to the patient that I’m a medical student :) * Believe it or not, you can establish a connection with the patient by breaking the ice with saying these few words. So it is important for you to identify yourself, so that the patient knows your name and sees your face to have a more personal relation. * Then you take the permission to touch the skin, this is the polite way! Some patients may reject that and say “NO”, so you should respect that and say “thank you”. * Also you should always maintain the patient’s privacy.
Now you have to take the patient’s story, and the first thing you have to think of is to take the chief complaint of the patient. When we say that the patient has rash, this means that the patient has multiple red things with or without scale. And when the patient says that he has a lesion, this means one or few things. And the patient may have other complaints like hair loss, blisters, color change … etc.
After you identify the chief complaint, you have to do a quick analysis of the chief complaint: * Onset and progression. * Modifying factors. * Symptoms: the most common symptom in dermatology is itching. Some itches may be painful. And this has a diagnostic indication, for example, herpes zoster infection is a famous painful infection. * In patients who present with rashes, we have to inquire about previous illnesses; viral, fevers, infections, that’s because the rash may happen because of the illness. * Atopy like in patients who have aczema, asthma, or hay fever, this is only relevant if it was in the patient himself or in a 1st degree relative (father, mother, brothers, sisters), other relatives are not important. * Drugs used.
Next we do a quick review to the systems and take the past medical history. In dermatology, we’re lucky that we see the disease, so we depend on a good description or a proper pathologic examination.

Derm Exam (TSAD)
Then we signified the TSAD exam (Type, Shape, Arrangement, and Distribution). * Type:
The 1st step in doing dermatologic examination is to identify the type, it’s not that easy, so you have to know the terminologies and the definitions. We have primary lesions and secondary lesions, we call them secondary lesions if they are modified by other factors, and the main factor is the patient himself when he scratches the primary lesion, so it becomes a secondary lesion.
Why is it important to identify the type? Because here is where formulating the differential diagnosis starts.
If somebody describes a primary lesion as being a macule, for example, that means that there is only an alteration in the color or the texture of the skin, but no elevation, and no depth. So we only see a color change or a textural change. We call it patch if the diameter is more than 2 cm, and the macule is less than 0.5 cm in diameter. Here we may think of a pigmentary disorder or a resolving papulosquampus condition as a differential diagnosis.
Papules and plaques: means that it is solid and elevated; you can feel the lesion if you close your eyes. If they were small; less than 0.5 cm in diameter, then we call them papules. If they were more than 2 cm we call them plaques.
And when the patient has scaly papules/plaques, we call that papulosquamous condition; eczema is the commonest example on that. When having non-scaly papules/plaques (elevated and red in color), it is called reactive erythema.
So the first step of formulating a differential diagnosis is by right identification of the type. So if somebody gives the right description -even if he consults the dermatologist on the phone-, he can know what he has, or at least he becomes oriented to a certain group of lesions.
This is just to illustrate the types of the lesions. (Refer to slides #13 & 14)
*Macule: you can see that there is only change in the color or the texture with no elevation.
*Papule: there is an elevation but no apparent depth.
*Nodule: its depth reaches the dermis.
Those have diagnostic indications, like when we have a pathology of thickening in the epidermis, we think of pure skin disorders. But if it is significantly more in the dermis (the pathology is more in the dermis) where we have blood vessels that may bring diseases from elsewhere in body, so we think of systemic causes.
*Pustule: it is accumulation of pus with a diameter less than 0.5 cm.
*Plaque: it is a solid elevation of the skin that is more than 2 cm in diameter.
*Scale: it is when there is an increase in the mitosis level of the basal cells, so lots of cells are going to the surface. Cells on the surface have to be desquamated (shed). Normally, we shed cells without realizing that, because cells are shed as single cells (each cell on its own). But when we have hyper-proliferation, the shedding will be in sheets (millions of cells together); this will be visible as a scale. Scales are a hallmark of a group of lesions called papulosquamous conditions.

* Shape:
Here we give more details of the primary lesion concerning the color, surface, and margins. * Color:

* If a lesion is red in color, this means there is blood. [The only thing in the human body which gives a red color is blood (hemoglobin in RBCs)]. This blood can be inside the blood vessels (dilated blood vessels because of inflammatory mediators like Histamine) or hemorrhage (extravasation as in vasculitis or bleeding tendency).

* If a lesion is brown or black in color, there is either increase in melanin or increase in the amount of melanocytes. This has good diagnostic implications.

* Yellow color comes from carotin. Carotin is present mainly in the subcutaneous fat and to some extent in the horney layer.
So there are only three natural colors (pigments) in the skin: brown or black (from melanin), red (from RBCs), and yellow (from carotin). If there is excess pigment of any of them, it will give the predominant color. * Surface:
When we look at the surface of the primary or secondary lesion, we have to see whether it is scaly or not. If it is scaly, then it belongs to the papulosquamous conditions; one of the biggest groups of lesions we see. If it is non-scaly, then it belongs to the group of reactive erythemas. * Margins:
Margins are either well-defined or ill-defined; and this is especially important for scaly conditions. * Arrangement:
How the primary lesions are arranged together. Sometimes they can be in a line (plane warts) or in vesicles (Herpes). * Distribution:
If something is generalized affecting the whole skin, we think of inflammatory conditions; they tend to be symmetrical and bilateral. If it is involving only part of the skin, we think of external causes: infection, contact allergy, or trauma. If it is on the sun-exposed parts like hands and face, we think of the sun (conditions like photodermatoses / photoaggravated dermatoses).

Red non-scaly rash
If a patient has a rash which is red and non-scaly, then it could be a reactive erythema. We have different types of reactive erythemas; the commonest ones are urticaria, erythema multiforme, and erythema nodosum.
Vasculitis is the only one of the non-scaly erythematous lesions that has hemorrhage. The other reactive erythemas are inflammatory conditions, so they are non-scaly and associated with dilated blood vessels.
If we have a red area, how do we know if it is due to hemorrhage or dilated blood vessels?
We do what we call "diascopy". We bring a glass slide and press it over the skin; if the color disappears, then the blood vessels are dilated and can be compressed, so it's not vasculitis. Vasculitis is associated with hemorrhage, so you can't push the RBCs back into the blood vessels.

We also look at the time limit.
Urticaria is one of the reactive erythemas caused by type 1 hypersensitivity reaction (IgE binding to an antigen). Each individual lesion of urticaria lasts up to 24 hours. Urticaria is one of the conditions easily diagnosed if you ask the appropriate questions (ask about the duration). If a patient tells you that his rash appeared in the morning and then faded away by night, then this is urticaria. The only lesion that comes and goes within 24 hours is urticaria.
Note that the whole disease may last (come & go) for many years. The duration of 24 hours is concerning the individual lesion. The lesion of urticaria is called a wheal.
Erythema multiforme is another reactive erythema in which lesions persist for one to two weeks. So if a patient has a red non-scaly rash that has been present for 4 days, can this be urticaria? No! If it is distributed on the acrofacial parts (face, hands, & feet), then it is typical erythema multiforme.
The other reactive erythema is erythema nodosum. Here the lesions stay for a longer time; for about 4 to 6 weeks (up to 8 weeks). They tend to affect the areas containing fat and the typical site is on the shins.

Case: If you have a patient with a red non-scaly rash, then you know it belongs to the reactive erythemas. But you have to exclude vasculitis, so you do diascopy. You bring a glass slide and press over the lesion and see if the color disappears; if it disappeared, then you exclude vasculitis. Then you ask about the duration the lesions persist; if it was about a week, you exclude urticaria. Then you ask about the site of the lesions; if on the face, neck, or hands, then most likely it is erythema multiforme.
These have certain underlying causes as you will know later on; for example, the most common underlying cause for erythema multiforme is Herpes virus infection, while the most common cause for urticaria in children is viral infection and in adults is drugs especially NSAIDs (aspirin, ibuprofen …). The most important underlying cause which we have to rule out in any patient presenting with erythema nodosum is TB. So any patient presenting with erythema nodosum we do for him chest x-ray and PPD.

Red scaly rash (papulosquamous)
Scale is flake (تقشر) of squamous.
This condition usually indicates hyper-proliferation of the epidermis; the “birth rate” of basal cells is high.
Flake of squamous group includes several conditions, the most common one is eczema followed by psoriasis (الصدفية).

Other conditions of papulosqamous group from the slides: * Lichen Planus * Fungal infections * Pityriasis Rosea

Case:
If a patient complained of rash with skin peeling, we have to think immediately about eczema and psoriasis because at least 90-95% of patients who came with such a condition have either eczema or psoriasis.

* Scaly rashes examination:

As we mentioned in examination we have to describe 3 things:
1) Color 2) Surface 3) Margins.

Margins are especially important in scaly conditions, because the scaly conditions eczema and psoriasis (the most common 2) can be easily differentiated by their margins.
Eczema has ill-defined margin; we can’t identify the borders easily.
Psoriasis has well- defined margin, we can easily identify the borders.

Case:
If a patient came with a scaly rash, we have to ask him about its margins, are they ill or well-defined?
If the margins were ill-defined, it’s eczema, and if they were well-defined, it’s psoriasis.

**The doctor said we don’t have to remember other conditions except eczema and psoriasis that can be differentiated by the margins.

Identify?!
This is a scaly rash with well-defined margins, then this is psoriasis.

If there was only one lesion on one arm or leg, then this is from an external source that caused infection.

Typical color for psoriasis is salmon pink color; between red and orange!

Scaly rash belongs to flake of squamous group, with ill-defined margins, so this is eczema.

And here in this picture (slide #25) appears the typical color for psoriasis, salmon pink color; between red and orange And this is one type from the flake of squamous group called Lichen Planus. In slide #26-28 we can see red non scaly conditions called reactive erythemas; can be vasculitis, erythema multiforme, erythema nodosum or urticaria. This patient slide #29, has red non scaly rash, when we do diascopy the color doesn’t disappear, this means that we have hemorrhage, so this can be vasculitis or a patient with bleeding tendency.

In reactive erythema conditions we ask about duration while in scaly conditions we look to the margin. If the patient had reactive erythema for 47 days; we can exclude urticaria and erythema multiforme, and this is most likely to be erythema nodosum. Investigations that should be done to this patient are chest x-ray, TB and other things! If we ask a patient with urticaria about the lesion he will say that it comes and disappears within 24 hours or less. Here we can see non-scaly lesions appeared one week ago, so it can’t be urticaria, when we do diascopy they disappear which means that they aren’t vasculitic, so the top differential diagnosis here is erythema multiforme. We should ask this patient if he had previous infection herpes simplex virus which is the most common cause.

Diagnostics:

* Wood’s light * KOH * Diascopy * Tzanck smear * IF (Direct: tissue and Indirect: plasma) * Patch Test

Slide #33: Fungal hyphae

**We have to do scrapping to the scaly skin if the flake of squamous was unilateral**
Done By:
Wesal Gharra, Basma Deeb, and Noor Abu Farsakh