Dermatology
USMLE
STEP 2
REVIEW
COPY-RIGHTED REVIEW
, Dermatology – USMLE STEP 2 REVIEW
Introduction
Skin lesions could be either at the level of the skin, elevated, or under the skin & others. The cut-off point of skin lesions is 5mm
Skin level lesions: Macule if <5mm & Patch if >5mm
SOLID elevated lesions: Papule if <5mm & Plaque if >5mm.., If the elevated lesion has fluid inside, it is called Vesicle if <5mm
& Bulla if >5mm.., If the elevated lesion has pus inside, it is Pustule
Under the skin lesions are called Nodules, which is seen to be elevated “exophytic” or palpated “endophytic”.
Red discolored lesions could be: Erythema: red discoloration, caused by vasodilation “can be bleached” & Prupura: red
discoloration, caused by vascular disruption “can NOT be bleached”, according to size, the latter is classified as petichea <
purpura < echymosis
Examination of all skin lesions follows the mnemonic T-SAD:
T: type “macule, papule… etc”
S: shape, by commenting on: size, color, borders “well\ill-defined” & surface “scaly or not. If elevated, comment on the elevation
type “irregular, plain… etc””
A: arrangement, if the lesions are arranged in such a way “linear, clusters… etc” or not
D: distribution, where does the lesions present
e.g.: a single medium sized patch, brown in color, well-defined borders,
non scaly, with no specific arrangement, present on the forearm
N.B: always examine mucus membranes, scalp & genital area
, Eczema “dermatitis”
Eczema: is a general term describing inflammation of the skin, which has many types, and may be acute or chronic.
Types of eczema: irritant contact dermatitis
Allergic contact dermatitis
Atopic dermatitis
Seborrheic dermatitis
Acute Chronic
Blistering “wet”* Less vesicular “dry”
Less scaly Scaly
Ill-defined papules & erythema Fissuring
Weeping & crusting Lichenification**
*Inflammation leads to edema between keratenocytes “spongeosis”, which eventually merge to make vesicle that ruptures
“weeps” giving the wet appearance, then the ruptured vesicle crusts.
**Thickening and increased markings of the skin; due to repeated scratching.
Acute eczema “note the vesicles”
Chronic eczema “note the dryness, scales & fissuring”
, Lichenification “note increased markings of the skin”
Irritant contact dermatitis: is more common “80%” than allergic contact dermatitis, and is the result of damage to the
keratenocytes when exposed to some agents “play dough, saliva, bubble-bath & chemicals… etc” WITHOUT an immunologic
reaction.
The reaction depends on the intensity of the irritant; the stronger “concentrated, longer time exposed”, the shorter time needed for
the reaction to appear.
Irritant dermatitis “due to lip licking “saliva””
Allergic contact dermatitis: is a type IV hypersensitivity reaction of the skin, due to exposure to some immunologically
irritating substances. It usually takes linear configuration “the shape of the allergen”
Allergic dermatitis due to contact with Nickel ring
N.B: both types of contact dermatitis should be suspected if:
Certain areas are involved “eyelids, external auditory meatus, hands\feet & around gravitational ulcers”
USMLE
STEP 2
REVIEW
COPY-RIGHTED REVIEW
, Dermatology – USMLE STEP 2 REVIEW
Introduction
Skin lesions could be either at the level of the skin, elevated, or under the skin & others. The cut-off point of skin lesions is 5mm
Skin level lesions: Macule if <5mm & Patch if >5mm
SOLID elevated lesions: Papule if <5mm & Plaque if >5mm.., If the elevated lesion has fluid inside, it is called Vesicle if <5mm
& Bulla if >5mm.., If the elevated lesion has pus inside, it is Pustule
Under the skin lesions are called Nodules, which is seen to be elevated “exophytic” or palpated “endophytic”.
Red discolored lesions could be: Erythema: red discoloration, caused by vasodilation “can be bleached” & Prupura: red
discoloration, caused by vascular disruption “can NOT be bleached”, according to size, the latter is classified as petichea <
purpura < echymosis
Examination of all skin lesions follows the mnemonic T-SAD:
T: type “macule, papule… etc”
S: shape, by commenting on: size, color, borders “well\ill-defined” & surface “scaly or not. If elevated, comment on the elevation
type “irregular, plain… etc””
A: arrangement, if the lesions are arranged in such a way “linear, clusters… etc” or not
D: distribution, where does the lesions present
e.g.: a single medium sized patch, brown in color, well-defined borders,
non scaly, with no specific arrangement, present on the forearm
N.B: always examine mucus membranes, scalp & genital area
, Eczema “dermatitis”
Eczema: is a general term describing inflammation of the skin, which has many types, and may be acute or chronic.
Types of eczema: irritant contact dermatitis
Allergic contact dermatitis
Atopic dermatitis
Seborrheic dermatitis
Acute Chronic
Blistering “wet”* Less vesicular “dry”
Less scaly Scaly
Ill-defined papules & erythema Fissuring
Weeping & crusting Lichenification**
*Inflammation leads to edema between keratenocytes “spongeosis”, which eventually merge to make vesicle that ruptures
“weeps” giving the wet appearance, then the ruptured vesicle crusts.
**Thickening and increased markings of the skin; due to repeated scratching.
Acute eczema “note the vesicles”
Chronic eczema “note the dryness, scales & fissuring”
, Lichenification “note increased markings of the skin”
Irritant contact dermatitis: is more common “80%” than allergic contact dermatitis, and is the result of damage to the
keratenocytes when exposed to some agents “play dough, saliva, bubble-bath & chemicals… etc” WITHOUT an immunologic
reaction.
The reaction depends on the intensity of the irritant; the stronger “concentrated, longer time exposed”, the shorter time needed for
the reaction to appear.
Irritant dermatitis “due to lip licking “saliva””
Allergic contact dermatitis: is a type IV hypersensitivity reaction of the skin, due to exposure to some immunologically
irritating substances. It usually takes linear configuration “the shape of the allergen”
Allergic dermatitis due to contact with Nickel ring
N.B: both types of contact dermatitis should be suspected if:
Certain areas are involved “eyelids, external auditory meatus, hands\feet & around gravitational ulcers”
