Infectious Myositis:

Infectious myositis is an uncommon acute, or chronic infection of skeletal muscle.

Most often seen in young adults.

The most common infectious agent is the bacterium, Staphylococcus aureus

(77-90% of Myositis cases) (prevalent in tropical countries).

Viruses, other bacteria (including Mycobacteria), fungi, and parasites can cause

myositis.

It consists of a primary abscess, edema, and hypoechoic inflammatory Mass.

Infectious Myositis

Infectious Myositis

Viral etiologies typically cause diffuse myositis, whereas bacteria and fungi

usually lead to a local myositis which may be associated with sites compromised

by trauma or surgery and are more common among immuno-compromised

patients.

Localized collections within the muscles are referred to as pyomyositis.

Other pyogenic causes of myositis include gas gangrene, group A Streptococcal

myonecrosis, and other types of non- Clostridial myonecrosis.

Bacterial pyomyositis: Pyomyositis consists of a primary muscle abscess and is prevalent in tropical countries.

It is associated mainly with immunocompromised patients, and intravenous drug abusers who traumatically contaminate their muscles with foreign material.

The clinical presentation is often

nonspecific with muscle aches

and cramps and a deep induration

and may at first suggest an

intramuscular neoplasm.

The causative agent is Staphylococcus

aureus in over 90% of cases.

Bacterial pyomyositis

Streptococcus Myonecrosis

Streptococcus Myonecrosis:

Streptococcal myositis is a rare, often fatal, acute infection of the muscle, caused by an invasive group A beta-haemolytic Streptococcus.

It is characterized by muscle necrosis without abscess formation, and, in contrast to necrotizing fasciitis, does not primarily affect the subcutaneous tissue or skin.

It is a predisposing factor for septic shock. Management:

1- Early diagnosis using emergency CT scans.

2- High-dose intravenous antibiotics.

3- Early aggressive surgical debridement.

4- Intensive fluid and nutritional support.

Streptococcal toxic shock syndrome.

Clostridium Myonecrosis: (Gas gangrene): Clostridial Myonecrosis is a bacterial infection that produces gas tissues in gangrene (necrotic damage of tissue specifically muscles).

It is a deadly form of gangrene usually caused by Clostridium perfringens bacteria.

This bacterium causes Myonecrosis via specific exotoxins .

In general, different clostridium species are opportunistic and enter the body via significant skin breakage.

The exotoxin is commonly found in C. perfringens type A strain and is known as alpha toxin.

Clostridium Myonecrosis

The alpha toxin is a phospholipase requiring zinc for activation.

First, The C-terminal domain binds calcium and allows the toxin to bind to the phospholipid head-groups on the cell surface.

The N-terminal domain has phospholipase activity.

This property allows hydrolysis of phospholipids such as phosphatidyl choline to diacylglycerol.

Clostridium Myonecrosis

The end result includes activation of arachidonic acid pathway

and production of thromboxane A2 (vasoconstrictor),

production of IL-8, platelet-activating factor, and several

intercellular adhesion molecules. These actions combine to

cause edema due to increased vascular permeability.

Clostridium Myonecrosis

Clinical picture of Clostridium perfringens :

Clostridium Myonecrosis

Tetanus ( lockjaw disease):

It is a medical condition characterized by a prolonged contraction of skeletal muscle fibers.

The primary symptoms are caused by tetanospasmin (A-light chain, B-heavy chain), a neurotoxin produced by the Clostridium tetani.

Infection occurs through wound contamination and often involves a cut or deep puncture wound.

Tetanus

As the infection progresses, muscle spasms develop in the jaw and elsewhere in the body.

Mortality rates reported vary from 48% to 73%.

In recent years, approximately 11% of reported tetanus cases have been fatal.

Pathophysiology: Tetanus begins when endospores of Clostridium tetani enter damaged tissue.

The spores transform into rod-shaped bacteria and produce the neurotoxin tetanospasmin.

This toxin is inactive inside the bacteria.

Tetanus

When the toxin is released , it will be activated by proteases.

Active tetanospasmin enters at neuromuscular junctions of motor neurons, B-chain (heavy) binds to neuronal membrane sphingolipid.

The light- A chain carried by axonal transport of peripheral nerve terminals to cell bodies in the spinal cord and brain stem where it binds to receptors at these sites.

Tetanus

- The A-chain, a zinc endopeptidase, attacks the vesicle-associated membrane protein of central nervous system neurons.

- The action of the A-chain stops the affected neurons (inhibitory synapses) from releasing the inhibitory neurotransmitters GABA (gamma-aminobutyric acid) and glycine by degrading the protein synaptobrevin.

- Result: consequence dangerous overactivity in the muscles from the smallest stimulus.

Clostridium tetani also produces an oxygen-labile hemolysin called tetanolysin.

Tetanus

Tetanus

Mechanism of action of Tetanospasmin toxin:

Forms of tetanus: On the basis of clinical symptoms, four different forms of tetanus have been described.

Generalized tetanus is the most common type of tetanus, representing about 80% of cases.

The generalized form usually presents with a descending pattern. The first sign is lockjaw, and the facial spasms called risus sardonicus (Sardonic smile), followed by stiffness of the neck, difficulty in swallowing, and rigidity of pectoral and calf muscles. Other symptoms include elevated temperature, sweating, elevated blood pressure, and cardiac arrhythmias.

Other forms: Neonatal , localized and cephalic tetanus.

Tetanus

Clinical picture of Clostridium tetani:

Tetanus

Muscle spasms in a patient suffering from tetanus. Neonatal Tetanus. Painting by Sir Charles Bell, 1809.

Facial spasms called Risus Sardonicus- First Symptom of Generalized Tetanus.

Laboratory diagnosis: Clinical specimens: Pus swab, exudate (thioglycolate media).

Tetanus

C. perfringens: Beta surrounded Beta hemolytic filamentous by Alpha hemolysis. C. tetani.

Parasitic Myositis: Trypanosoma cruzi : Transmission : when the Winged bug  of the genus Triatoma deposits feces on the skin surface and subsequently bites; the human host.

Late ( chronic) stage infection: affects the nervous system, digestive system and cardiac muscle. The protozoa will infect Skeletal muscle

by its Amastigote stage.

Amastigote stage in skeletal muscle

Parasitic Myositis

Trichinella spiralis:It is a nematode parasite, occurring in rats, pigs, and humans, and is responsible for the disease trichinosis.

Humans typically become infected when they eat improperly cooked pork (Trichinella infected) meat.

Female Trichinella worms stay for about six weeks, in small intestine, and in that time can produce up to 1,500 larvae. Larvae will migrate with blood to striated muscles causing myositis.

The muscles invaded mainly are: pectoral and intercostal muscles, tongue, the diaphragm, and the gastrocnemius.

Parasitic Myositis

Cysticercosis:Cysticercosis involves infection of individuals with the larval stage of

Taenia solium, the cysticerci, which normally infects pigs.

Autoinfection may occur due to fecal-oral transmission.

The oncosphere ( hexacantho-embryo) penetrates the intestinal wall and migrates in the circulation to the tissue ( skeletal muscles).

Parasitic Myositis

Rabies:Virology:

The rabies virus is the type species of the Lyssavirus genus, in the family Rhabdoviridae.

Lyssaviruses have helical symmetry, with a length of about 180 nm and a cross-sectional diameter of about 75 nm. These viruses are enveloped and have a single-stranded RNA genome

Electron microscopy

Show the helical

Enveloped single stranded

RNA virus.

Viral Myositis

Rabies is a viral disease that causes acute encephalitis (inflammation of the brain) in warm-blooded animals.

The virus is usually present in the nerves and saliva of a symptomatic rabid animal. The route of infection is usually, but not always, by a bite.

The infection is initiated by inoculation of virus into skeletal muscles, virus will be replicated in muscle and transferred to peripheral nervous system.

The rabies virus travels to the brain by following the peripheral nerves.

Rabies kills around 55,000 people a year, mostly in Asia and Africa (2010).

Viral Myositis

Viral Myositis