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Additional attention during examination should fo- these lesions. It is very easy to superficially look at le-
cus on the finger and toenails. Is there discoloration, sions and miss the fact that they do not blanch. The
cracking, or changes in the nail itself? Check if there is absence of blanching is important because it indicates
involvement of the mucous membranes, and if there are that there has been hemorrhage into the skin. If your
any palpable lymph nodes. What is the overall appear- examination reveals petechiae, the clinician must ensure
ance of the patient, do they look unwell? As always, it is that there is not a serious underlying medical condition.
important to take the vital signs. Figure 3 outlines an algorithm to diagnose an unknown
petechial rash.
The Case
The Algorithm
After carefully studying the patient, you determine that
the rash is distributed on her lower extremities. You After determining the primary lesion is petechial, the
note that the rash does not blanch and that some of the next step is to determine if the patient is febrile or ap-
lesions are palpable (Box 2). She has a little pain with pears toxic. Do they look sick? Do they have abnormal
range of motion of her knees, but there is no swelling. vital signs? This leads to the next branching point. Are
You determine that the primary lesions are petechiae. the lesions palpable? When you run your fingers across
There are some large areas of purpura and coalesced the skin, do the lesions feel raised or knotty in the skin?
petechiae. The patient does not appear distressed. Her Typically, palpable lesions indicate that an inflammatory
vital signs are unremarkable. or infectious condition has irritated the blood vessels
within the skin. This further subdivides the algorithm
1
and helps you narrow your differential diagnosis. Once
BOX 2 BLANCHING you arrive at your differential diagnoses, you can use
When all color drains from a lesion as it is compressed. your history, physical examination findings, and knowl-
This can be seen by apply a fingertip to a lesion and then edge base to zero in on the diagnosis. This is important
removing it. If there is any doubt, a clear plastic or glass because some of these illness require urgent treatment.
surface can be used. A glass slide works great if available.
Looking through the algorithm, you can see that there
Identifying petechial lesions is critical because there are are a few very serious diagnoses on this list! A com-
a number of serious medical conditions associated with plete review of all these conditions is beyond the scope

Figure 3 The algorithmic approach to the petechial/purpuric rash.

Image used with permission of Heather Murphy-Lavoie.

78 Journal of Special Operations Medicine Volume 16, Edition 1/Spring 2016