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Have developed red itchy bumps on inner thigh and behind knees. Underlying cause?

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Practicing since : 2006
Answered : 2016 Questions
I have developed overnight red bumps on inner thigh and behind knees. They are less raised this morning but know bright red. The bumps are relatively symmetrical left to right. I slept in hotel last night and itching woke me up.
Posted Thu, 8 Aug 2013 in Skin Hair and Nails
Answered by Dr. Kalpana Pathak 12 minutes later
Thanks for writing to us.
from the description provided, there could be two possibilities
Urticaria - it presents as wheals or sometimes as small raised bumps or just red blotches which are itchy. The lesions can be symmetrical and urticaria has a nocturnal tendency too. The lesions are transient and evanescent and tend to disappear on its own after sometime

Insect bite.

Allergic rash

The treatment in all the cases more or less remains the same. Take an oral antihistamine like cetirizine. It would help the rash subside and relieve itch. Also apply calamine lotion mixed with a steroid lotion twice in a day.
Urticaria would subside in a day. Insect bite or allergic rash would need couple of days.

Hope that answered your query.
Take care
Above answer was peer-reviewed by
Follow-up: Have developed red itchy bumps on inner thigh and behind knees. Underlying cause? 2 days later
Follow up. The bumps seems to be slowly improving and many are turning into pimples. Although two bumps by my ankles have clear fluid filled sacs. Is this normal? Do you have ability to view photos?
Thank you
Answered by Dr. Kalpana Pathak 13 minutes later

Thanks for writing back.

I would definitely love to view the images of concerned lesions as in dermatology diagnosis depends majorly on clinical examination of lesion.

You may upload a good resolution image by clicking on report image/ report icon which is on query page. You may also send the pictures to YYYY@YYYY and mention attn: dr kalpana in subject line.

Hoping to receive the images soon.
Take care
Above answer was peer-reviewed by
Follow-up: Have developed red itchy bumps on inner thigh and behind knees. Underlying cause? 1 hour later
I will send 3 separate emails via phone now
Answered by Dr. Kalpana Pathak 11 hours later
Thanks for sending the images. from the images attached, it looks like you could be having chicken pox as fluid filled lesions can be seen over red base. Similar lesions can sometimes occur with insect bite too. But if you are having any systemic symptoms like fever, bodyache malaise, cough etc chances are it could be chicken pox. Similarly if lesions are occuring all over the body, it is chicken pox.
In adult age group it could be serious, so I would advise that you visit a doctor nearby and get your diagnosis confirmed. If it is chicken pox, please take a course of oral antiviral like acyclovir or valacyclovir along with an oral antibiotic. Bathe everyday with antibacterial soap and apply topical antibacterial cream to help the lesion heal fast. If itching is there take oral antihistamine. Take light meals, maintain hydration and take adequate rest.
Hope that helped.
Take care
Above answer was peer-reviewed by
Follow-up: Have developed red itchy bumps on inner thigh and behind knees. Underlying cause? 6 hours later
Hi Dr. Kalpana

Thank you for your response. I do NOT have any systemic symptoms and the lesions are isolated to lower extremities only. As well, they are getting better day by day.

I just have 2 last questions for you:

1. Out of curiosity, do you feel that ONE insect bite cause an allergic reaction, hives?

My theory on why behind my knees are are the worst, (largest most pronounced) lesions.

When I woke up in the middle of the I had 2-3 bumps, similar to mosquito bites on my thigh. I was concerned about bed bugs from this motel so I put on my jeans and slept in a chair. When I woke up the next morning I could feel the binding and bunching up of the jeans behind my knees, as I slept with my legs flexed. Similar to fetal position.

This caused the fluid from the histamine release to pool in concentration behind my knees, thus it will take longer for the body to reabsorb.

2. What are your thoughts?

Thank you so much!
Answered by Dr. Kalpana Pathak 23 hours later
Please accept my apologies for responding so late.
To answer your question specifically.
Yes a single insect bite can lead to profuse allergic reaction, urticaria, even angioedema to an extent that a person can be fatally breathless and collapse. Now having said this in your case if we consider these lesions are of insect bite then in that case you might have had multiple bites.

The blistering that occurs in insect bite is not due to released histamine but due to a toxin produced by an insect( canthiridin is one such toxin). So as such let us suppose that an insect bit you behind the knee and left its toxin there. Now due to your flexed position the toxin led to maximum damage in the concerned area. Clinically we get cases of blistering insect bites but usually the lesions are not all so discrete as are seen in your case, instead initially lesions form a long trail at one site and rest of the few lesions are discrete( as you did not post a pic of area behind your knee, so i cant really comment, however you may google blister beetle dermatitis to understand what i mean to say).

As you do not have fever and no other systemic complaints with your lesion limited to extremity, We will have to rule chicken pox out. However the lesions are like CP only. Another possibility is herpes zoster, but again the lesions are discrete and not grouped.

So now insect bite appears to be a diagnosis of exclusion. Just use a good steroid antiubiotic cream over the lesion to help it heal faster.
But if in case you develop more lesions then please consult a dermatologist nearby. Differentiating chicken pox and insect bite or herpes zoster is so easy when you XXXXXXX a patient face to face, but when it is an online consultation you have to cautious.
Hope that helped.
Take care
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