What are some clues to help distinguish viral from drug-induced exanthems?

It is often difficult to distinguish but here are some clues ...

• viral exanthems often have associated fever, malaise, sore throat and conjunctivitis; although drug reactions may have these features also
• viral exanthems happen more frequently in children; although adults can get them too 
• a rash that develops within 3 days of a drug being initiated for an infection is more likely secondary to the infection because of the time required for hypersensitivity to develop in a patient not previously sensitized to a particular drug

Selected infections and Other Conditions that Often Include an Exanthem and Characteristics that Help Differentiate Them from an Exanthematous Drug Eruption.  (click image to enlarge)

Source

 Stern, R.  "Exanthematous Drug Eruptions"  NEJM.  28 June 2012.

What lesion differentiates scabies from other rashes?

A curved or linear burrow about 1 to 10 mm long (caused by the movement of the mite in the stratum corneum) that often ends in a tiny papule or pustule.



Source

Marco, C. and Soleimani, M.  "Cutaneous Infestations"  Critical Decisions in Emergency Medicine.  Jan 2013.

Image Source: http://www.bpac.org.nz/magazine/2009/february/scabies.asp

What is optimal treatment for treatment of IV contrast soft tissue infiltration?

There is no known proven way to ameliorate potential soft tissue injury. Avoid excessive heat or cold, injection of steroids or other agents which have no known benefit. Treat skin necrosis if it occurs.


Source

Roberts: Clinical Procedures in Emergency Medicine, 5th ed.

Can adults get HSP (Henoch-Schonlein Purpura)?

Yes but it's rare. If a patient > 20 y/o presents with palpable purpura to the lower extremities, it is more likely to be a hypersensitivity vasculitis whereby immune complexes are deposited in venules as a result of infections, drugs, neoplasms, autoimmune connective tissue disease, or dysproteinemias. Treatment is with prednisone +/- antibiotics, for patients in whom this vasculitis follows a bacterial infection. Other disease entities to include in the differential include thrombocytopenic purpura, DIC, septic vasculitis (rickettsial spotted fevers), septic emboli (infective endocarditis), bacteremia (disseminated gonococcal infection, meningococcemia) and other vasculitides.


Source

Fitzpatrick's Color Atlas & Synopsis of Clinical Dermatology

Image source: http://www.hdcn.com/symp/lund/jtimg26.jpg

18 y/o ill-appearing male presents with this rash. Other than supportive care, what four additional treatments should be considered?

A generalized eruption manifested by macules and papules

1. doxycycline: Rocky Mountain Spotted Fever

• incidence highest 5 - 9 y/o
  
• transmitted by tick, although only 60% have knowledge of recent tick bite
• organisms attach to vascular endothelial cells causing generalized vasculitis
  
• occurs only in western hemisphere; in US highest incidence in Oklahoma, North Carolina, Virginia, Maryland, Georgia, Michigan, Alaska, Montana, South Dakota
  
• fever, severe headache, myalgias
• early lesions are blanchable macules which then evolve into deep red non-blanchable, papules; rash characteristically spreads centripetally

2. doxycycline: Ehrlichiosis

• tick borne illness
• while Ehrlichiosis is often known as Rocky Mountain Spotted fever without the rash, this is only partially true, as a small minority of patients will have a macularpapular exanthem
  
• for more information regarding ehrlichiosis, see previous posts, here and here
  

3. penicillin G benzathine (or doxycycline): Secondary Syphilis

• appears 2 - 6 months after primary infection
• may also see condylomata lata: soft, flat-topped, moist, red-to-pale papules, nodules or plaques
  

4. ceftriaxone: Meningococcemia

• incidence highest 6 months - 3 years
  
• 50 - 80% with meningococcemia develop meningitis
• early lesions are sparsely distributed macules/papules which then evolve into petechiae/purpura
  

5. ceftriaxone: Disseminated Gonococcal Infection

• gonococcus disseminates from infected mucosal site and a affects skin and joints
  
• erythematous macules evolve into hemorrhagic pustules, acral (peripheral) body parts more affected

6. ceftriaxone: Typhoid fever

• febrile illness with non-specific abdominal pain and rash 5 - 21 days after ingestion of salmonella in contaminated food or water, often after foreign travel
  
• rash is faint salmon colored macules on trunk and abdomen (rose spots)
  

7. penicillin G benzathine (or ceftriaxone): Scarlet Fever

• site of group A strep infection: pharynx, infected surgical or other wound
  
• rash appears 1 - 3 days after onset of infection
  
• begins with finely punctate erythema on the upper truck which becomes confluently erythematous. Rash is accentuated in skin folds (Pastia's lines). Exanthem fades within 4 - 5 days and is followed by desquamation
  

8. steroids: Drug Hypersensitivity Syndrome

• most commonly a reaction to antiepileptic drugs and sulfonamides
• onset generally 2 - 6 weeks after initiation of drug
  
• eosinophilia or presense of atypical lymphocytes
  
• potential systemic involvement: lymphadenopathy, interstitial nephritis, interstitial pneumonititis, carditis

9. steroids: Graft-Verus-Host Disease

• most commonly seen with allogeneic bone marrow transplantation. Less often with autologous bone marrow transplantation or blood transfusion

10. amphotericin B: systemic fungal infection with dissemination to skin

• consider in immunocompromised host
  

Bottom Line: In a sick patient with maculo-papular rash, consider empiric treatment with doxycycline, ceftriaxone, steroids and/or amphotericin B to cover the above disease entities in addition to standard supportive measures which should cover erythema infectiosum (parvovirus B19), cytomegalovirus, epstein-barr virus, herpes virus type 6, measles, german measles, echovirus, coxsackie, adenovirus.


Source

Fitzpatrick's Color Atlas & Synopsis of Clinical Dermatology. 5th ed.

Image source: http://www.aafp.org/afp/20050615/2323_f1.jpg

What's the treatment of this rash: painless papular lesions in perineum of sexually active male?

Scroll Down For Answer

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Molluscum Contagiosum

Treatment: In healthy individuals, lesions heal spontaneously but this may take up to 2 years. In immunocompromised individuals lesions often don't resolve spontaneously and aggressive treatments (curettage, cryosurgery) should be considered.

Etiology: molluscum contagiosum virus spread by skin to skin contact

Physical Exam: papules, pearly white or skin-colored, central keratotic plug which gives lesion a central dimple; gentle pressure on a molluscum causes the central plug to be extruded

Source
Fitzpatrick's Color Atlas & Synopsis of Clinical Dermatology, 5th ed

Image: "Source: Bárbara Pereira MD, Dermatology Online Journal "

How can one distinguish erythema migrans (EM) from a simple non-specific bug bite reaction?

The following suggest EM:

History: running about brushy, wooded, grassy habitat during late May through early fall (in midwestern and eastern United States) or January through May (in Pacific Northwest) w/ EM type rash developing 3 - 32 days later; history of tick attachment > 18 hours

Physical Exam: expanding annular lesion which may have several rings of varying shades of red, center may be indurated, vesicular or necrotic, maximum median diameter is 15 cm (rather large); can be associated with burning sensation, itching, or pain.

Diagnosis: Classic EM does not need serologic confirmation. In equivocal cases, serologic testing may be considered. IgM antibodies appear within 1-2 weeks and IgG antibodies within 2-6 weeks following onset of EM and can be detected using a sensitive (although not specific) ELISA assay and confirmed with Western blotting.

Of note, antibodies often remain elevated despite therapy and resolution of symptoms.

Source

Fitzpatrick's Color Atlas & Synopsis of Clinical Dermatology, 5th ed.

Sexton, Daniel MD. "Diagnosis of Lyme disease" Up to Date. <http://www.uptodate.com>