Ephelides

Synonym(s)

Freckles

Epidemic typhus 209

Definition

Tan macules which darken after sun exposure and fade in the winter months

Epidemic typhus

Pathogenesis

Autosomal dominant trait; possibly somatic mutations in epidermal melanocytes that promote increased melanogenesis

Clinical manifestation

Multiple, small, uniformly tan macules on sun-exposed skin; sometimes coalescing into patches; most common in individuals with fair skin and/or blond or red hair

Differential diagnosis

Lentigo; seborrheic keratosis; nevus; café au lait spot; tinea versicolor

Therapy

Sun avoidance

Synonym(s)

Louse-borne typhus; classic typhus Definition

Acute, febrile, infectious illness caused by Rickettsia prowazekii, characterized by rash, lymphadenopathy, and systemic signs and symptoms

Pathogenesis

Caused by Rickettsia prowazekii; louse infected after feeding on rickettsemic person with typhus or during a recrudescent case; bites human to engage in blood meal and causes pruritic reaction on host skin; scratching by host causes crushing of lice and Rickettsia-laden excrement inoculated into wound

References

Ortonne JP (1990) The effects of ultraviolet exposure on skin melanin pigmentation. Journal of International Medical Research 18 Suppl 3:8C-17C

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