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What can be dx

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"fever" AND "urticaria" AND children

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PMID: 38026129

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PMID: 39104358

Summary of the Case

Yatharth, 1 yr 3 mo male, 9.15 kg presented with:
  • Fever x 5 days (101.2°F), rash noted by the pediatrician as urticaria
  • Exam: alert (AVPU-A), chest clear, no other findings documented
  • CBC: WBC 8.05 x10³/µL (normal), differential essentially unremarkable; Hb 9.5 g/dL (low), Hct 30% (low), MCV 68.3 fL (low), MCH 21.7 pg (low) -> microcytic, hypochromic picture; Platelets 357 x10³/µL (mildly high)
  • CRP 44.7 mg/L (markedly elevated, ref <1)
  • Typhidot IgM was sent (pending/awaited) and the doctor has asked to "review with report"
This is not a single confirmed diagnosis yet - the treating pediatrician (Dr. Deepak Kumar) is actively working it up. Based on the pattern of findings, here is the reasonable differential:

Most Likely: Viral fever with urticarial exanthem / "Urticaria multiforme"

At this age, fever accompanied by an urticarial rash is most commonly a post-viral or para-infectious urticaria, sometimes called urticaria multiforme (annular/target-like urticarial plaques mistaken for erythema multiforme). It typically occurs in children under 7, follows a febrile viral illness, and blood work shows only mild inflammatory changes - which matches this child's picture (normal WBC, non-specifically elevated CRP). It is benign and self-limiting, resolving within days to weeks with antihistamines +/- a short antibiotic course if a bacterial trigger is suspected (Kan SY et al., J Paediatr Child Health 2024, PMID 39104358; Sekerel BE et al., Front Allergy 2023, PMID 38026129).

Other diagnoses being actively considered/ruled out

  1. Enteric (typhoid) fever - explains why Typhidot IgM was sent. Fits fever duration and raised CRP, though typhoid is less common under age 2 and the rash of typhoid (rose spots) is not typically urticarial - Sleisenger & Fordtran's GI/Liver Disease and Park's Textbook of PSM both describe prolonged step-ladder fever with relative bradycardia/hepatosplenomegaly as classic features, which aren't documented here.
  2. Drug-induced urticaria - if any antibiotic/antipyretic was started before this visit, urticaria can be a hypersensitivity reaction rather than infection-driven (well described even with amoxicillin-clavulanate causing fever + urticaria in young children, PMID 36415045).
  3. Kawasaki disease (incomplete) - a "cannot-miss" diagnosis in any child with fever ≥5 days plus rash, especially with reactive thrombocytosis and high CRP as seen here. Classic diagnostic criteria (conjunctival injection, oral/lip changes, extremity edema/desquamation, cervical lymphadenopathy, polymorphous rash) were not documented in the note, but with fever now at day 5 this should be specifically examined for on follow-up, since missed Kawasaki risks coronary artery involvement.
  4. Other febrile viral exanthems / arboviral illness - roseola, adenovirus, EBV, parvovirus B19, or (given Ranchi/Jharkhand, monsoon season) dengue or scrub typhus, both of which commonly cause fever + rash + elevated CRP regionally and should be considered if Typhidot and routine workup are negative.
  5. Underlying iron deficiency anemia (Hb 9.5, MCV 68.3, MCH 21.7 - microcytic hypochromic) - almost certainly a separate, pre-existing nutritional issue common at this age ("milk anemia of infancy" from prolonged milk feeding without iron-rich weaning foods), not related to the acute febrile illness, but worth a peripheral smear and iron studies on follow-up.

What determines the final diagnosis

  • Typhidot IgM result (pending) - positive supports enteric fever
  • Clinical re-examination for Kawasaki criteria (eyes, lips/tongue, hands/feet, neck nodes) - important given fever duration
  • History of any new drug exposure before rash onset
  • Consider dengue NS1/malaria smear/scrub typhus serology if fever persists and Typhidot is negative
  • Iron studies/peripheral smear for the anemia (separate issue)
Recent evidence check: no new systematic reviews/meta-analyses in the last 2 years specifically contradict this reasoning; the cited PMIDs (38026129, 39104358) are the closest relevant recent literature on pediatric fever-associated urticaria.
This is meant to help you understand the possibilities the doctor is working through - it does not replace follow-up with Dr. Deepak Kumar, who already has the full clinical picture and the pending Typhidot result. Please follow up with him as advised on the prescription ("review with report").

Typhoid negative

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"incomplete Kawasaki disease" infant diagnosis

Good - that rules out enteric fever from the differential. Here's the updated picture:

Updated Differential (Typhoid excluded)

With Typhidot IgM negative, and the child having: fever x5 days, urticarial rash, elevated CRP (44.7), and reactive thrombocytosis (Platelets 357, upper end/mildly high) with a normal WBC, the two leading possibilities now are:

1. Viral-triggered acute urticaria / "urticaria multiforme" (most likely)

Still the most probable explanation. A preceding or concurrent viral infection (very common in toddlers) triggering an urticarial exanthem fits this labs pattern almost exactly: normal WBC, mild-moderate CRP elevation, benign self-limited course. This resolves within days to a few weeks with antihistamines +/- antipyretics, no further workup usually needed (Kan SY et al., J Paediatr Child Health 2024, PMID 39104358).

2. Incomplete/atypical Kawasaki disease - now more important to actively exclude

This becomes the key "cannot-miss" diagnosis to rule out now that the obvious infective cause (typhoid) is negative. Per the Harriet Lane Handbook and Red Book (AAP Committee on Infectious Diseases):
  • Classic KD = fever ≥5 days + 4 of 5 principal criteria: bilateral non-exudative conjunctival injection, oral/lip changes (cracked lips, strawberry tongue, erythema), polymorphous rash, extremity changes (edema/erythema of hands/feet, later periungual desquamation), cervical lymphadenopathy (>1.5 cm)
  • Incomplete KD should be suspected in any infant/child with unexplained fever ≥5 days who does not meet all classic criteria, especially in infants <1 year (who are at higher risk of atypical presentation and coronary artery involvement) - this describes Yatharth almost exactly (age 1y3m, fever day 5, rash, elevated inflammatory markers, no clear infective cause found so far).
  • Supportive lab findings for incomplete KD: CRP ≥3 mg/dL (this child is at 44.7 mg/L = 4.47 mg/dL, above threshold), elevated platelets after day 7 of illness (still normal-ish now but trending up), anemia, sterile pyuria, elevated ALT, low albumin.
  • Echocardiogram is the key next step if KD is suspected, since coronary artery changes can occur even in incomplete presentations.
Recent literature (PMID 35308689, 40161185, 40747178 - all infant case reports 2022-2025) consistently emphasizes that infants under 1 year with fever and rash are the group most likely to be missed for incomplete KD because they present with fewer classic features, yet carry higher risk of coronary complications, so a low threshold for echo and cardiology referral is recommended.

3. Drug-induced urticaria

Still worth asking whether any antibiotic or antipyretic was started just before the rash appeared, as this can mimic infection-driven urticaria.

4. Other viral exanthems / regional considerations

Given the Ranchi/Jharkhand location and August (monsoon) timing, dengue and scrub typhus remain reasonable considerations if fever persists beyond another day or two without clear explanation.

Practical next step

Since typhoid is now excluded and fever has reached day 5 (the KD threshold), the most clinically important action is for the treating pediatrician to specifically re-examine for the 5 principal Kawasaki criteria (eyes, lips/mouth, hands/feet, neck nodes, rash character) on the follow-up visit already scheduled, and consider an echocardiogram if any are present or if fever continues without another clear cause, given the elevated CRP and reactive thrombocytosis already seen. This is something to flag directly to Dr. Deepak Kumar at the review visit rather than manage at home, since incomplete Kawasaki disease in infants is time-sensitive (treatment with IVIG is most effective within 10 days of fever onset to prevent coronary artery aneurysms).
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