SKIN, SOFT TISSUE, AND BONE INFECTIONSClinical Correlation Series

impetigo

Ecthyma

Cellulitis

Panniculitis

Necrotizing fasciitis

Erysipelas

CONSIDERATIONS IN SKIN AND SOFT TISSUE INFECTIONLocalization – layer(s) of tissue involvedLocalized vs. multifocal; disseminated vs.

symmetricalAcute, (bright red, warm, tender) vs. chronic or

subacute (dusky red, indurated older eschar or ulcer along with papules)

Deep involvement, e.g. muscle (pyomyositis, osteomyelitis, panniculitis

Hematogenous vs. exogenousHost factors, exposures

GENERAL RULES IN SKIN INFECTION

Pustules, tender painful papule or nodule with fluctuance –pyogenic esp. StaphSpreading erythema, painful , recent onset – Strep, PasteurellaBites – cat (Pasteurella), dog (Capnocytophaga), human (Eikenella)Linear nodules – Tularemia, Mycobacterium, Sporothrix, NocardiaVesicles – Herpes, RickettsialpoxSystemic toxicity, pain out of proportion to appearance –Necrotizing fasciitisBullae – Vibrio, Capnocytophaga, CampylobacterGangrene – Polymicrobial including Clostridia, enteric GNREschar – Molds, anthrax, tick borne, septicemiaPurpura – Meningococcus, Strep, StaphPetechiae – Rickettsia, CMV,EBV, HIV (acute)

INFECTION

Mastectomy Group A strepFish Tank M. marinumFresh water AeromonasThorn, moss SporothrixNeutropenic, moist area PseudomonasNeutropenic, tender nodules CandidaSplenectomy CapnocytophagaCirrhosis VibrioPalms, soles Syphilis, RickettsiaEschar Molds, anthrax, RickettsiaLymphadenopathy Bartonella, Tularemia

Finding Organism(s)

SKIN INFECTION: GEOGRAPHIC FACTORS

Lyme disease (Erythema chronicum migrans)Blastomycosis (Ulcerated, verrucous, plaques)Yersinia pestis (Southwest US)Coccidioides (Erythema nodosum)Ehrlichia (RMSF-like illness)Vibrio, mycobacteria (Gulf coast)Leishmania (middle east vets)

FEVER AND RASH: LIFE THREATENING ASSOCIATIONS

Petechial lesions - meningococcal, rickettsialsepsis, TTP*

Mucosal involvement – Stevens-Johnson syndromeBullae – Toxic epidermal necrolysis, VibrioPurpura – meningococcus, staph, strep, or

pneumococus (purpura fulminans) Ecthyma gangrenosum – Gram negative sepsisDigital infarcts – Catastrophic APS**, DIC,***

Capnocytophaga, meningococcus

• *thrombotic, thrombocytopenic purpura• **antiphospholipid antibody syndrome• ***disseminated intravascular coagulation

MISCELLANEOUS CLUES TO ETIOLOGY OF SKIN INFECTION

Urticaria – hepatitis B (autoimmune reaction)Slapped cheek, sock and glove purpura –ParvovirusHemorrhagic pustules – NeisseriaNail puncture foot – PseudomonasAmoxicillin – EBVChronic severe atopy, severe burns – HSVIntrathoracic or intraabdominal involvement –Actinomycosis, TBUnderlying osteomyelitis – S. aureus, BartonellaLung and /or CNS involvement – Nocardia, endemic mycoses, mycobacteria

FEVER AND RASH: IMPORTANT CONSIDERATIONS

History must include risk factor assessment –concurrent diseases, medication, travel, occupational/recreational exposure, animalsThorough exam including entire skin area, mucosa, lymph nodesInfectious and non infectious diseases can coexistSkin biopsy for culture and histology rarely contraindicated Acute retroviral syndrome self-inflicted lesions often not considered

INDICATIONS FOR BIOPSY, FURTHER TESTING PRIOR TO RX FOR FEBRILE RASH

Chronic or recurrent natureUlceration, indurationFailure to respond to seemingly appropriate RxWorsening on RxImmunocompromised host, trauma, any factor suggesting non infectious causeConcurrent disease elsewhere, where skin biopsy much less risky than other tissue

SOME USEFUL TESTS FOR FEVER AND RASH EVALUATION

CXR Mycoplasma, vasculitisCryptococcal antigen AIDS, transplant and feverCBC with differential Drug reaction, parasiteHIV Fever, rash, nodesRPR Palm/sole rashANA, ANCA Arthralgia, renal diseaseSerology for RMSF, Ehrlichia Petechiae, headacheSPEP Pyoderma gangrenosumLFT Urticaria, headache,

petechiaBlood culture Petechia, toxicity,

immunocompromised

Test Suspected etiology,clinical setting

Echthyma – S. aureus

STREPTOCOCCAL ECTHYMA

Carbuncle – S. aureus

Erysipelas

Anthrax

Purpura due to Meningococcus

Pyogenic Cellulitis

Linear, Nodular Lesions: SporotrichoidMycobacteriosis

INFECTIONS OF BONE

LOCALIZATION OF ACUTE, HEMATOGENOUS OSTEOMYELITIS

Arterial blood flows to blind loop sinusoids

CLASSIFICATION OF OSTEOMYELITISPathophysiologic

Acute vs. chronicHematogenous vs. contiguous/traumatic

Therapeutically Based MedullarySuperficialCortical LocalizedDiffuse

OSTEOMYELITIS

medullarysuperficial

localized diffuse

SYMPTOMS OF OSTEOMYELITISPain – esp. hematogenous (pediatric, vertebral)

may be exquisite or vaguemay signal complication, e.g. spread to

epidural spaceindistinguishable from sickle cell pain

crisisFever - uncommon

SIGNS OF OSTEOMYELITISErythema, edema, necrosis, bullae, crepitancePurulence, sinus tractNon-healing ulcer: cause or consequenceVisible bone (decubitus ulcer)Non–union of fractureSeparation of components (joint prosthesis)Elevated WBC, platelets, sedimentation rate , normocytic anemia (of chronic disease)Radiologic findings

PATHOPHYSIOLOGY OF OSTEOMYELITIS

Hematogenous – anatomically abnormal bone, prostheses, metaphyses ,vertebral end plate have either increased blood flow a nidus for infectionContiguous – loss of soft tissue barrier, direct traumaMSCRAMM – microbial surface components that recognize adhesive matrix moleculesBacteria adherent to devitalized bone much more resistant to antibiotics

ETIOLOGIES OF OSTEOMYELITISAcute – S. aureus; Salmonella with sickle diseaseContiguous – skin flora; polymicrobial (fecal flora for decubiti, staph strep, anaerobes for diabetes)Immunocompromised – mycobacteria, fungi, pseudomonasProstheses related – Coagulase positive and negative staph, diphtheroidsVertebral – S. aureus, tuberculosis, endocarditispathogens

SEQUESTRUM OF CHRONIC OSTEOMYELITIS

Devitalized bone

MEDULLARRY (HEMATOGENOUS) OSYEOMYELITIS

Resorbed bone adjacent to growth plate

OSTEBLASTIC RESPONSE TO CHRONIC OSTEOMYELITIS

Hyperdense calcification (involucrum)

MR imaging for osteomyelitis

Marrow edema

Loss of bone

VERTEBRAL OSTEOMYELITIS WITH EPIDURAL COMPRESSION

DIABETIC FOOT ULCER -OSTEOMYELITIS

DIAGNOSTIC PITFALLS IN OSTEOMYELITIS

Imaging may lag in acute settingsImaging may distinguish post surgical or traumatic changesCultures may reflect surface contaminantsBiopsy may yield sampling errorNuclear studies may reflect sterile inflammation due to adjacent soft tissueNeuropathy, decubiti may mask painGenerally, MR most sensitive, x-rays lag 2 or more weeks behind, negative nuclear studies helpful

RX OF OSTEOMYELITISHematogenous often cured with antibiotic aloneChronic types esp if cortical or diffuse, prosthesis related, non-union fracture, diabetes related need debridementPolymicrobial consideration for trauma, contiguous etiologyUsually 6 weeks IV Rx, followed by weeks to months oral agent

MUSCLE INFECTIONQuite rare in absence of trauma, ischemiaS. aureus pyomyositis – HIV related in U.S., no obvious risk in tropicsPsoas abscess – relatively common complication of vertebral osteomyelitis (TB, S.aureus)Parasites – trichinosisViral – influenzae B, but not clinically significantClostridia – part of fulminant septic picture in setting of underlying malignancy

PSOAS ABSCESS

Pyomyositis, ring enhancing lesion