Skin nontumor
Dermal perivascular and vasculopathic reaction patterns
Arthropod bites
Last author update: 1 May 2016
Last staff update: 20 February 2024 (update in progress)
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PubMed Search: Arthropod bite
Table of Contents
Definition / general | Essential features | Sites | Clinical features | Treatment | Clinical images | Microscopic (histologic) description | Microscopic (histologic) images | Differential diagnosis | Additional referencesCite this page: Perkins IU, Gardner JM, Stuart LN. Arthropod bites. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/skinnontumorarthropod.html. Accessed April 23rd, 2024.
Definition / general
- Seen in all age groups in various cutaneous sites
- Caused by fleas, bed bugs, biting flies, mosquitoes, ants, ticks and spiders
- Most bites are clinically self limited and not biopsied
- Bites from brown recluse and black widow spiders have the greatest potential morbidity, causing necrosis requiring operative debridement and occasionally amputation
Essential features
- Variable clinical presentation from erythematous papule to nodular lesion with induration, ulceration and vesicles
- Often self limited; extensive or persistent cutaneous reactions may be treated with intralesional steroids
- Typically manifests microscopically with a mixed infiltrate of lymphocytes, histiocytes and eosinophils
- Exuberant cases with dense deep lymphocyte rich infiltrate may mimic a low grade lymphoma
- Spider bites often show necrosis and vasculitis
Sites
- Variable, relating to site of exposure, including:
- Flea bites: ankles
- Mosquito bites: exposed skin
- Chigger bites: socks and belt lines
Clinical features
- Varied clinical presentation ranging from small clusters of erythematous papules to large deep violaceous nodules with induration, ulceration or vesicles
- May resemble lymphoma or ulcerated carcinoma
- A solitary punctum may be found at the site where insect mouth parts contact the skin
- Spider bites may have necrosis with nonviable tissue present at the ulcer base
Treatment
- Most bites are self limited
- Antihistamines may provide symptomatic relief
- Severe mosquito reactions ("Skeeter syndrome") may require prednisone (Am Fam Physician 2013;88:841)
Clinical images
Images hosted on other servers:
Various images
Microscopic (histologic) description
- Typically wedge shaped superficial and deep mixed inflammatory infiltrate composed of lymphocytes, histiocytes, eosinophils and sometimes neutrophils
- Scattered eosinophils in interstitial areas (away from vessels), especially in deep dermis, are a useful clue
- May also have a prominent granulomatous component
- Dermal edema commonly seen; vessels may be prominent
- Variable epidermal features including spongiosis, acanthosis, parakeratosis; these are most prominent in center of lesion where mouth parts penetrate the epidermis
- Excoriated lesions may have prominent parakeratosis with scale crust formation, epidermal erosion or overt ulceration
- May have lymphoid germinal centers resembling lymphoma, with destruction of adnexae, particularly sweat glands (J Cutan Pathol 2009;36:26)
- Mouth parts may be identified in center of lesion, particularly in tick bites
- May have secondary vasculitis
- Spider bites: often show marked necrosis with extensive suppurative neutrophilic dermal inflammation, often extending into underlying subcutaneous tissue; small and large vessel vasculitis is also common
- Fire ant stings:
- Acute phase: may be characterized by an urticarial reaction
- Later stages: mixed inflammatory infiltrate consisting of eosinophils and neutrophilic pustules
Microscopic (histologic) images
Images hosted on other servers:
Wedge shaped and perivascular inflammatory infiltrate of lymphocytes and eosinophils
Differential diagnosis
- Allergic contact dermatitis: may occasionally have increased eosinophils but infiltrate is usually mostly in superficial not deep dermis; often has more broad epidermal changes including spongiosis, parakeratosis and Langerhans cell microabscesses; necrosis and vasculitis are uncommon
- Eosinophilic folliculitis: perifollicular infiltrate with numerous eosinophils; may be associated with HIV and thus diagnosis should be made with caution; clinical correlation very important
- Dermal hypersensitivity reaction (e.g. drug eruption): can have very similar appearance to arthropod bite reaction; clinical correlation is best way to separate; presence of epidermal changes or wedge shaped infiltrate may favor arthropod bite
- Lymphomatoid papulosis: scattered or numerous CD30+ atypical lymphocytes
- Well's syndrome (eosinophilic cellulitis): can have very similar appearance; superficial and deep infiltrate with eosinophils that may be so numerous that they degranulate, and free granules coat degenerated collagen bundles ("flame figures")
- Well's syndrome is a diagnosis of exclusion - must rule out arthropod bite reaction (may have flame figures) and drug eruption clinically
Additional references
