Differential Diagnoses of Common Presentations

Question 1

Brown Macule.

Inflammatory

Answer 1

Post-inflammatory

hyperpigmentation

Question 2

Brown Macule. Drug/Toxin

Answer 2

UV radiation, actinic/solar

lentigo, freckle (ephelide)

Question 3

Brown Macule. Miscellaneous (Congenital, Neoplasia, Other)

Answer 3

Congenital: café-au-lait spots, congenital nevus, epidermal/junctional
nevus
Neoplasia: lentigo maligna, MM, pigmented BCC
Other: melasma/chloasma (“mask of pregnancy”)

Question 4

Discrete Red

Papule. Infectious

Answer 4

Folliculitis
Furuncle
Scabies

Question 5

Discrete Red

Papule. Inflammatory

Answer 5

Acne vulgaris
Rosacea
Psoriasis
Urticaria

Question 6

Discrete Red

Papule Drug/Toxin

Answer 6

Bites/stings

Question 7

Discrete Red

Papule. Miscellaneous (Autoimmune, Vascular, Other)

Answer 7

Autoimmune: lichen planus; see Papulosquamous Diseases, D16
Vascular: hemangioma, pyogenic granuloma
Other: dermatofibroma, miliaria rubra

Question 8

Red Scales. Infectious

Answer 8

Pityriasis rosea
Secondary syphilis
Tinea

Question 9

Red Scales. Inflammatory

Answer 9

Dermatitis (atopic, contact,
nummular, seborrheic)
Discoid lupus
Psoriasis

Question 10

Red Scales. Drug/Toxin

Answer 10

Gold

Question 11

Red Scales. Miscellaneous (Autoimmune, Neoplastic)

Answer 11

Autoimmune: lichen planus; see Papulosquamous Diseases, D16
Neoplastic: mycosis fungoides

Question 12

Vesicle. Infectious

Answer 12

Cat scratch disease
Impetigo
Viral: HSV, HZV, VZV,
Molluscum, Coxsackie,
Scabies

Question 13

Vesicle. Inflammatory

Answer 13

Acute contact dermatitis

Dyshidrotic eczema

Question 14

Vesicle. Drug/Toxin

Answer 14

none

Question 15

Vesicle. Miscellaneous

Answer 15

Other: dermatitis herpetiformis, porphyria cutanea tarda

Question 16

Bulla. Infectious

Answer 16

Bullous impetigo

Question 17

Bulla Inflammatory

Answer 17

Acute dermatitis

EM, SLE, SJS/TEN

Question 18

Bulla Drug/Toxin

Answer 18

Fixed drug eruption

SJS/TEN

Question 19

Bulla Miscellaneous

Answer 19

Autoimmune: bullous pemphigoid, pemphigus vulgaris
Other: dermatitis herpetiformis, porphyria cutanea tarda

Question 20

Pustule Infectious

Answer 20

Candida
Dermatophyte
Impetigo
Sepsis
Varicella

Question 21

Pustule Inflammatory

Answer 21

Acne vulgaris
Rosacea
Dyshidrotic dermatitis
Pustular folliculitis
Pustular psoriasis
Hidradenitis suppurativa

Question 22

Pustule Drug/Toxin

Answer 22

Acute generalized
exanthematous pustulosis
(usually secondary to drug
reaction)

Question 23

Oral Ulcer. Infectious

Answer 23

Aspergillosis
CMV
Coxsackie
Cryptococcosis
HSV/HZV
HIV, TB, Syphilis

Question 24

Oral Ulcer Inflammatory

Answer 24

Allergic stomatitis
EM
Lichen planus
Seronegative arthropathies, SLE
Recurrent aphthous stomatitis
Behçet’s disease

Question 25

Oral Ulcer Drug/Toxin

Answer 25

Chemotherapy
Radiation therapy
SJS/TEN

Question 26

Oral Ulcer Miscellaneous.Autoimmune, Congenital,Hematologic, Neoplasia

Answer 26

Autoimmune: pemphigus vulgaris
Congenital: XXY
Hematologic: sickle cell disease
Neoplasia: BCC, SCC

Question 27

Skin Ulcer Infectious

Answer 27

Plague
Syphilis
TB
Tularemia

Question 28

Skin Ulcer Inflammatory

Answer 28

RA, SLE, vasculitis

UC (pyoderma gangrenosum)

Question 29

Skin Ulcer Miscellaneous

Answer 29

Autoimmune: necrobiosis lipoidica diabeticorum (e.g. DM)
Congenital: XXY
Hematologic: sickle cell disease
Neoplasia: SCC
Vascular: arterial, neurotrophic, pressure, venous, aphthous, leukoplakia,
traumatic