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[deleted] t1_ivnn9ug wrote

Reply to comment by killcat in In House M. D. there is an episode in which the doc asked the lady who was concerned about weight gain. Doc asked her to raise their hand and by seeing that he was able to determine she was pregnant. Do arms and pregnancy have some correlation? by Abhinav_Mani

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spacemanv t1_ivnsogw wrote

It actually does tend to appear very close to the initial bite within the first week. It then spreads after that.

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Watsonmolly t1_ivny3k2 wrote

but surely the lymph nodes near the initial bite, that's why its often the back of the knee.

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spacemanv t1_ivnzdhm wrote

The first rash is actually immediately over the bite in 70% of cases, and is a immune mediated superficial skin rash. It actually gets it's characteristic bullseye shape from the center being an immune reaction to the salivary proteins, and the outer ring being the spread of bacteria outwards in the skin. You see them behind the knees because it's easy for ticks to get brushed into skin folds.

The secondary (stage 2) lesions and lymphadenopathy happen after the bacteria spreads from the initial lesion in the weeks following.

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