5 types of mechanical injury
Abrasions, contusions, lacerations, incised wounds and puncture wounds
A patient presents with a skin lesion and only the epidermal layer is removed. What type of mechanical injury is this?
A patient presents with a skin lesion that shows extravasation of blood into surrounding tissue. What type of mechanical injury is this?
A patient presents with a skin lesion that shows tearing of tissues, jagged edges and intact blood vessels and nerves. What type of mechanical injury is this?
A patient presents with a skin lesion that shows tearing of tissues, defined borders and severed blood vessels. What type of mechanical injury is this?
When is a puncture wound termed as penetrating vs. perforating?
Penetrating = entrance wound. Perforating = entrance and exit wound.
What factors determine the clinical significance of a thermal burn injury?
Depth, percentage of body surface, internal injury and promptness of treatment.
A patient presents with a thermal burn confined to the epidermis. What type of burn is this?
A patient presents with a thermal burn confined to the dermis and epidermis. Its gross appearance is pink and blistery and is very painful. Histology reveals coagulative necrosis and marked exudation. What type of burn is this?
Partial thickness burn. Note that nerve endings are spared and the lesion is very painful.
A patient presents with a thermal burn that affects the subcutaneous tissue and muscle. Its gross appearance is white, dry and the patient cannot feel anything at the wound site. Histologic examination reveals coagulative necrosis and marked exudation. What type of burn is this?
Full-thickness burn. Note that these are anesthetic because full nerves are lost.
Greatest threats to life in patients with thermal burn injuries
Shock, sepsis and respiratory insufficiency
What is responsible for the hypovolemic shock seen in patients with burns that cover at least 20% of body surface?
Fluid rapidly shifts to the interstitial spaces because plasma protein is lost. This results in generalized edema.
How does the resting metabolic rate change in someone with extensive burns?
It increases and the patient loses lots of heat and burns a lot of calories.
Common infections associated with burn injuries due to loss of blood flow and blockade of inflammatory response?
Pseudomonas aeruginosa is most common. S. aureus and Candida may also be involved.
Why might a patient who sustained a burn injury begin to suffocate 24-48 hours after the injury?
Inhalation of Cl, S and NH3 react with water to form alkalis and acids that cause inflammation in the airway that lead to obstruction.
Why might a patient who sustained a burn injury get pneumonitis deeper in the lungs?
Inhalation of NO from burning plastic
What is responsible for the constant itching at the site of injury burn victims feel for years after the injury?
Release of excess neuropeptides like substance P at the injury site results in hypertrophic scarring that itches.
Heat injury that often occurs in athletes due to loss of electrolytes
Heat injury that often occurs as a result of water depletion and hypovolemia. How do people recover?
Heat exhaustion. Collapse and prostration results in spontaneous recovery.
Heat injury that occurs as a result of thermoregulatory mechanism failure
Heat stroke. Sweating ceases and marked vasodilation causes peripheral pooling of blood which can result in hyperkalemia, tachycardia and arrhythmias.
What is responsible for the necrosis of muscle in people who get heat stroke?
Nitrosylation of the ryanodine receptor type 1 (RYR1)
Why are alcoholics at increased risk for hypothermia
The superficial blood vessels dilate even in cold temperatures and allow heat to escape.
When does loss of consciousness, atrial fibrillation and bradycardia begin in people with hypothermia?
Body temperature of 90 degrees
Direct effects of hypothermia
Cell lysis from high salt concentration due to crystallization of water
What is responsible for the edema, ischemia and hypoxia that occur in hypothermia?
Vasoconstriction and increased vascular permeability cause edema and hypoxia, but are only evident upon rewarming. Ischemia is a result of increased blood viscosity.
Where are you most likely to have an electrical injury that results in tetanic muscle spasm, irreversible clenching, chest wall muscle spasms and asphyxia?
In a home with alternating current electricity.
Where are you most likely to have an electrical injury that results in paralysis of the medullary centers and extensive burns?
High voltage from lightening
How are our cells affected by UV light, infrared light, microwaves and sound waves?
These are all types of non-ionizing radiation and only cause our atoms to vibrate.
How are our cells affected by x-rays, gamma rays, high-energy neutrons, alpha particles and beta particles?
These are all types of ionizing radiation and can directly damage DNA or displace electrons that produce ROS that damage DNA. Cells can then either repair themselves and go on, or they don’t repair themselves and die or don’t repair themselves and become cancerous. Note that alpha particles are most damaging.
Radioactive disintigrations per second
Radioactive energy absorbed by target tissue per unit mass
Gray (Gy) and Rads (1 cGy)
Radioactive energy that depends on the biologic effect of the radiation
Tissues with highest susceptibility to damage by ionizing radiation
Those that divide rapidly:gonads (leading to sterility), bone marrow (leading to marrow aplasia and anemia), lymphoid tissue (shrinkage of nodes and spleen) and GI mucosa.
What types of tumors will respond poorly to ionizing radiation?
Those with poor blood supply. This is because there is less oxygen around to form ROS and damage DNA.
Vascular changes associated with radiation
Interstitial fibrosis, endothelial cell swelling and vacuolization and hyalinization that can occur years later.
Nuclear changes seen with radiation
Chromosomal changes, clumping and nuclear swelling
Cytoplasmic changes seen with radiation.
Cytoplasmic swelling, mitochondrial distortion and ER degeneration
How does radiation commonly affect the lungs and salivary glands?
Vascular damage, loss of stem cells and the release of cytokines that promote inflammation stimulates fibroblast proliferation and causes radiation-induced fibrosis. Note that the colorectal and pelvic areas can also be affected this way.
Most serious DNA damage caused by radiation? How is this most often repaired? What implications does this have for the patient?
Double-stranded breaks. Most often repaired by the non homologous end joining (NHEJ) pathway. This pathway often produces deletions, duplications and chromosomal aberrations that may initiate carcinogenesis of cell replication is not stopped. These cells can also produce growth factors and cytokines that can be carcinogenic to the surrounding cells (bystander effect)
Second cancers that are often a result of radiation therapy
AML, myelodysplastic syndrome, Hodgkin lymphoma and solid tumors
Why is radon gas so good at causing lung cancer?
Its decay products polonium 214 and 218 deposit in the lung and emit alpha particles.
Gram positive cocci that form clusters
Pathogen involved in opportunistic infections in catheterized patients and patients with prosthetic valves
S. epidermidis, these have a polysaccharide capsule that allow them to adhere to artificial surfaces and resist phagocytosis.
Pathogen involved in female UTIs and opportunistic infections in IV drug users
What are the virulence factors associated with S. aureus?
Clumping factor: binds fibrinogen as a bridge to endothelial cells. Lipase: degrades skin lipids and produces abscesses. Protein A: bind Ig Fc region to escape opsonization. Alpha toxin: depolarizes host cell membranes by forming pores in them. Beta toxin: sphingomyelinase. Delta toxin: Detergent peptide. Gamma toxin: lyses erythrocytes. Leukocidin: lyses leukocytes. Exfoliative A/B toxins: cleaves desmoglein and separates keratinocytes. Superantigen:binds MHC and TCRs to activate T-cells, release cytokines and cause Toxic Shock Syndrome.
A patient presents with hypotension, renal failure, coagulopathy, liver disease, respiratory distress, a generalized erythematous rash and soft tissue necrosis around an abscess on the buttocks. Labs show a gram positive cocci in clusters. What is causing his condition?
Toxic shock syndrome from S. Aureus superantigen.
Staph infection restricted to the epidermis
Impetigo, note that this is not restricted to hair follicles.
Focal suppurative inflammation of the skin and subcutaneous tissue in moist, hairy areas like the face, axillae, groin, legs and submammary folds caused by staph infection
A growing, deepening abscess that comes to a head and ruptures in the overlying skin, caused by staph
A deeper suppurative infection that spreads laterally beneath the deep subcutaneous fascia and burrows superficially to cause multiple adjacent skin sinuses, caused by staph.
Chronic suppurative infection of apocrine gland in the axilla caused by staph.
Infections of the nail bed caused by staph
Infection of the palmar finger tips caused by staph
Felons. Note that these may follow trauma from a splinter.
How do people typically get staphylococcal lung infection?
A child presents with a sunburn-like rash that spreads over the body, has fragile bullae and skin desquamation at the granulosa layer of the epidermis. What is your diagnosis?
Scaled skin syndrome (Ritter disease). Note that toxic epidermal necrolysis (Lyell’s disease) from drug hypersensitivity cause desquamation at the level of the dermal-epidermal junction.
What antibiotics is MRSA resistant to?
Beta-lactams (PCN and cephalosporins)
Gram-positive cocci that grow in pairs and chains.
Streptococci and enterococci
Beta hemolytic gram positive cocci that grow in pairs and chains. What diseases can these pathogens cause?
Group A strep (strep pyogenes): pharyngitis, scarlet fever, erysipelas, impetigo, rheumatic fever, TSS and glomerulonephritis. Group B strep (strep agalactiae): sepsis and meningitis in neonates and chorioamnionitis in pregnancy.
Alpha hemolytic gram positive cocci that grow in pairs and chains. What disease can these pathogens cause?
Strep pneumo: adult meningitis and pneumonia. Normal flora: endocarditis. Strep mutans: dental caries.
Gram positive cocci that grow in chains, are resistant to many common antibiotics and commonly cause UTIs and endocarditis.
What are the virulence factors associated with streptococci?
S. pyogenes, S. agalactiae and S. pneumo all have capsules. S. pyogenes: M protein: prevents phagocytosis, C5a peptidase: degrades chemotactic peptide, exotoxin: fever and rash in scarlet fever. S. pneumo: pneumolysin: inserts into cell membranes and lyses them. S. mutans: plaque formation and conversion of sucrose to lactic acid.
A middle aged woman from Florida prints with rapidly spreading erythematous cutaneous swelling on the face. The rash has sharp serpiginous borders and forms a butterfly distribution. Histologic examination shows microabscesses and PMNs. What is your diagnosis?
Erysipelas from strep. pyogenes.
A patient presents with edema, epiglottic swelling, cervical lymphadenopathy and punctate abscesses in the tonsillar crypts. What complications is this patient at risk for?
He has streptococcal pharyngitis. This puts him at risk for suffocation (epiglottitis) and post streptococcal glomerulonephritis.
A 10year old presents with a punctate erythematous rash over the trunk and inner aspects of the arms and legs. She also has circumoral pallor. What is the most likely diagnosis?
Scarlet fever from strep pyogenes.
A patient presents with a tough, dirty gray to black superficial membrane on the oropharynx. PMN infiltration is intense. Labs show a gram positive rod with clubbed ends. What is causing his condition? How do you treat him?
C. diphtheria has a phage-encoded A-B toxin that ADP-ribosylates EF-2. You treat him with antitoxin.
What systemic effects are a result of diphtheria toxin?
Splenomegaly, lymphadenopathy, polyneuritis, myofiber necrosis and fatty change in the liver, kidney and adrenal glands.
Gram positive facultative intracellular bacilli
People most susceptible to listeria infection
Pregnant women, neonates, elderly and immunosuppressed
Diseases caused by listeria
Amnionitis and meningitis
Virulence factors associated with listeria
Internalin: binds E-cadherin on host epithelial cells and internalizes. Listeriolysin O: escapes phagolysosome. ACTA: induces actin polymerization to adjacent cells.
What immune response is most effective in eliminating listeria infection?
IFN-gamma produced by NK and T cells that activates macrophages
Rash that comes with listeria sepsis
Papular red rash
A farmer presents with painless, pruritic papules after working with raw hide and wool. The vesicles show striking surrounding edema and black eschar ulcers on ruptured vesicles. Physical exam reveals regional lymphadenopathy. Lab reveals a boxcar shaped gram positive rod. What is your diagnosis?
Bacilllus anthraces that causes cutaneous anthrax.
A patient presents with fever, cough and chest pain about a week after working with raw hid and wool. The next day he has abrupt onset of fever, hypoxia, sweating and meningitis. CXR reveals perihylar pneumonia and mediastinal hemorrhage. LP reveals boxcar shaped gram positive rods. He dies 2 days later. What is causing his condition?
Bacillus anthraces that causes inhalation anthrax.
A patient presents with nausea, abdominal pain, vomiting and bloody diarrhea. He ate raw meat before symptoms began and dies a few days after symptoms onset. Labs show a boxcar-shaped gram positive rod. What is causing his condition?
Bacillus anthraces that causes GI anthrax.
What virulence factors are associated with anthrax?
Polyglutamyl capsule: antiphagocytic. B toxin subunit: binds to cell and forms a pore in response to low pH, also a target of antibody. A toxin EF subunit: binds calmodulin and Ca2+ and forms adenylate cyclase, cAMP and induces water efflux to cause interstitial edema. A toxin LF subunit: destroys MAPKKs.
A patient presents with fever, weight loss and cough for the past 6 months. Screening tests for Tb and malignancy are negative. History reveals diabetes and HIV. Sputum culture reveals a slender gram positive organism with branching filaments and beaded appearance. What is likely causing this patient’s condition?
Nocardia asteroides is found in soil and is an opportunistic infection in patients with HIV and diabetes because they have depressed T-cell immunity. Note that 1/5 of Nocardia asteroides infects the CNS too.
A patient presents with rapidly progressive skin lesions. Histology shows a suppurative response with central liquefaction and surrounding granulation and fibrosis. Labs show a gram positive organism with branching filaments and a beaded appearance. What is causing his condition?
Nocardia brasiliensis infects the skin.
30-year-old male involved in a fatal motorcycle accident. No helmet was worn. The patient died despite aggressive life-saving intervention. A forensic pathologist performed the autopsy on the decedent, which showed numerous external blunt force injuries including a broken left leg. Internal examination identified liver and spleen lacerations, atlanto-occipital joint dislocation, and coup/contrecoup brain contusions. Toxicology results were negative for illicit drugs or alcohol consumption. Cause of death was listed as “Blunt Force Injuries” and manner of death “Accident.” One of his injuries is shown below. What might these injuries indicate?
The facial abrasion may indicate intracranial injury like diffuse axonal injury. The shoulder contusion may indicate the atlanto-occipital dislocation.
A 45-year-old man was a victim of a hit-and-run accident on an isolated road in Delaware . It took three days to find the body along the roadside in a shallow ditch. The decedent did not have proper ID in his wallet. A forensic autopsy was performed on the severely decomposed body. The cause of death was determined to be “Blunt Force Injuries involving the head, torso, and extremities”. “Manner of death “Homicide.” What are the stages of decomposition the body likely went through?
1) Green discoloration due to colonic bacteria denaturing hemoglobin with H2S to produce green biliverdin. 2) Marbling: bacteria move into blood vessels and H2S react with Hgb to form green-purple biliverdin. 3) Putrefaction: bloated abdomen, skin slippage and degloving of hand.
A 49-year-old man was beaten to death by his son after the father refused to give his son cash to support his son’s drug habit. After beating his father on the lower extremities with an iron skillet, he hit his father on the head with the skillet. The father was still conscious and attempted to call for 911 for help. The son then manually strangled him to death. A forensic autopsy was performed. The cause of death was determined to be “Asphyxia by manual strangulation associated with blunt force injuries.” Manner of death “Homicide.” What types of injuries would you expect to find on autopsy?
Contusions, lacerations and conjunctival petechiae from strangulation induces capillary rupture.
Police found this unresponsive 35-year-old male on the kitchen floor after being notified by a neighbor’s compliant of domestic violence. Next to the victim was a blood covered Phillips screwdriver and a kitchen knife having a 6” blade, but with a broken tip. A forensic autopsy is performed by the medical examiner. Tip of the knife was found on x-ray, wedged deep in the heart and sternum. Multiple defense wounds were identified on the back of the hands and arms. The decedent’s girlfriend is in custody after she confessed to murder while in a blind rage after discovering her boyfriend was unfaithful. What will differentiate the stab wounds you see from the incisions you see?
Stab wound are deeper than they are wide. Incisions are wider than they are deep. Neither of them have tissue bridges within them.
35 year old male US Navy Ensign undergoing superficial radiation therapy for pruritis ani et scrota; accidently exposed to several thousand roentgens of radiation at 50KV due to equipment operator error. Five year history of intractable anal and scrotal itching that has not responded to antibiotics, steroids, pinworm treatment or other topical treatments. WBC: 1,200 Platelets: 40,000 HCT: 25%. Why might he be at risk for radiation lymphedema?
Radiation kills lymphocytes and shrinks lymph nodes, which reduces lymph nod drainage.
A 45-year-old postal worker presents to her physician complaining of fever, myalgia, malaise, fatigue, retrosternal pain, and a nonproductive cough. She is diagnosed with a viral URI and sent home with a non- steroidal anti-inflammatory drug and a decongestant. Two days later, she is taken to the local emergency room with high fever, dyspnea, tachypnea, cyanosis, and chest pain. Chest X-ray in the ER demonstrates a widened mediastinum, paratracheal and hilar fullness, and pleural effusions. Peripheral blood smear is shown below. What is your diagnosis?
Note the boxcar-shaped gram positive rods that indicates B. antracis.
Which region of this brain was likely the “coup” region?
The front. The lesion on the back is likely the contra coup lesion.
Tissue least susceptible to ionizing radiation
Brain, neurons are not dividing
How might someone have colon problems if they receive radiation for testicular cancer?
A common effect of radiation is colonic stricture.
Adverse short and long term effects of ionizing radiation?
Fibrosis, mutagenesis, carcinogenesis and teratogenesis.
Early changes after radiation
Sterility, hematopoietic depression, pulmonary edema, GI mucosal injury/ulceration and skin erythema.
Late changes after radiation
Skin dyspigmentation/atrophy, pulmonary interstitial fibrosis, lymph node fibrosis, GI fibrosis, adhesions, keloid formation and sterility.
What cells would you expect to see in the alveoli of a patient with inhalation anthrax?
Hemosiderin-laiden macrophages from alveolar hemorrhage.
What gram positive cocci that grows in clusters can cause this?
Staph can cause osteomyelitis in kids.