Smallpox is most frequently misdiagnosed as varicella,
or chickenpox, which is caused by a herpes virus. The most
effective criteria for distinguishing the two infections is
an examination of the following characteristics of the lesions:
- Time and pattern of appearance: The most obvious
distinction between the two infections involves the time
period over which the skin lesions appear. In chickenpox
infection, the lesions occur in successive "crops". It is
possible, when examining a patient, to observe several
different stages of lesion maturation and development
at the same time. In smallpox infection the lesions
appear more or less simultaneously.
- Density and location: Chickenpox lesions tend
to be denser over the trunk (centrifugal distribution),
while smallpox lesions are denser on the face and extremities
(centripetal distribution). Chickenpox lesions are almost never
seen on the palms or soles of the feet. Smallpox lesions,
especially in severe cases, can often be found in these areas.
- Physiology: Chickenpox lesions tend to be superficial,
while smallpox lesions are much deeper, affecting the sebaceous
glands and leaving pitted, fibromatous scars.
Monkeypox is another infection to be considered in the
differential diagnosis of smallpox infection. Patients with
monkeypox develop fever, respiratory symptoms, and synchronized
lesions like patients with smallpox. However, patients with
monkeypox seem more prone to develop inguinal and cervical
lymphadenopathy and appear to have a lower mortality rate (3%-10%).
Pneumonia secondary to monkeypox has a 50% mortality rate.
The CDC has prepared a poster to assist in the differential
diagnosis of smallpox.
The poster has two parts.
Contents: Smallpox (Extensive Information)
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