Skeletal Muscle and Peripheral Nerve Pathology

Question 1

Characteristics of polymyositis

Answer 1

Autoimmune disease seen in adults

It presents with bilateral proximal muscle weakness.

Microscopic exam demonstrates endomysial lymphocytic inflammation (mostly cytotoxic T8) and skeletal muscle fiber degeneration and regeneration

Question 2

Characteristics of dermatomyositis

Answer 2

Connective tissue disorder involving inflammation of skeletal muscle and skin.

It can affect both children and adults.

It presents with bilateral proximal muscle weakness, skin rash of the upper eyelids and periorbital edema

Microscopic exam shows perimysial and vascular lymphocytic inflammation, perifascular fiber atrophy, and skeletal muscle fiber degeneration and regeneration

Question 3

Characteristics of inclusion body myositis

Answer 3

Affects adults age>50

Causes slowly preogressive, asymmetrical distal muscle weakness.

Light microscopic shows autophagic vaculoes and inclusion bodies in addition to inflammation and necrosis

Question 4

Characteristics of myasthenia gravis

Answer 4

Autoimmune disease characterized by autoiantibodies against the acetylcholine (ACh) receptor of the neuromuscular junction,resulting in muscular weakness predominantely affecting the facial muscles.

Females are affected more than males

Extraocular muscle weakness may lead to ptosis and diplopia; the weakness worsens with repeated contractions

Respiratory muscle involvement may lead to death

Question 5

What is mysathenia gravis associated with?

Answer 5

Thymic hyperplasia

Thymomas

Question 6

Characteristics of Lambert-Eaton syndrome

Answer 6

Frequently arises before a diagnosis of cancer is made, often in cases of small cell lung cancer

Patients report dry mouth and proximal muscle weakness.

Autoantibodies are directed against presynaptic calcium channels of the neuromuscular junction

Question 7

Characteristics of Duchenne muscular dsytrophy

Answer 7

It is the most common and severe form of muscular dystrophy.

Affected boys are normal at birth but have onset of symptoms by age 5.

Clinical features:
Progressive muscular weakness
Calf pseudohypertrophy
Proximal weakness of shoulder and pelvic girdles
Possible heart failure and arrhythmias
Respiratory insufficiency and pulmonary infections as a result of decreased mucociliary clearance

Question 8

What is the genetic inheritance of Duchenne muscular dystrophy?

Answer 8

Recessive X-linked form of muscular dystrophy leading to rapid progression of muscle degeneration.

The affected gene is the dystrophin gene on the X chromosome.

Mutation results in a virtual absence of the dystrophin protein

Question 9

Characteristics of Becker muscular dystrophy

Answer 9

Recessive X-linked inherited disorder leading to slowly progressive muscle weakness of the legs and pelvis

Less severe than Duchenne
Not as common as Duchenne
Has a later onset than Duchenne, with variable progression
Mutation produces an altered dystrophin protein
Cardiac involvement is rare and patients can have relatively normal lifespan

Question 10

Characteristics of lipoma

Answer 10

Benign adipose tissue tumor that most often arises in subcutaneous tissue of trunk, neck or proximal extremities.

It is the most common benign soft tissue tumor

Microscopically it is composed of mature fat cells but can contain other mesenchymal elements

Question 11

Characteristics of liposarcoma

Answer 11

Malignant adipose tissue tumor that most often arises in the thigh or retroperitoneum

It is the most commonadult sarcoma.

It is distinguised from lipoma by the presence of lipoblasts

Grossly it tends to be larger than lipoma and the cut surface shows fibrous bands

Microscopically well-differentiated liposarcoma consists of mature fat with varying numbers of hyperchromatic spindle cells and multivacuolated lipoblasts

Question 12

Characteristics of dermatofibroma

Answer 12

Benign dermal spindle cell proliferation that most often arises in the extremities

A small, red nodule is seen, which is tender and mobile on examination

Question 13

Characteristics of fibromatosis

Answer 13

Non-neoplastic proliferative connective tissue disorder that can histologically resemble a sarcoma

Fibrous tissue infiltrates muscle or other tissue and may cause a mass lesion. The cut surface is trabeculated

Microscopically bundles of fibroblasts and collagen are seen

Question 14

Characteristics of superficial fibromatoses

Answer 14

Arise from fascia or aponeuroses

Palmar fibromastosis is the most common type.

Question 15

Characteristics of deep fibromatoses

Answer 15

Occur in extraabdominal sites (children) and abdominal wall and extraabdominal sites (adults)

Abdominal desmoids often occur in women within a year of pregnancy.

They may also follow surgery or trauma

Question 16

Characteristics of fibrosarcoma

Answer 16

Malignant fibrous tumor, commonly seen on the thigh and upper limb.

It may arise spontaneously or after therapeutic/accidental irradiation.

Microscopically there are uniform spindle cells with a “herringbone” pattern.

Metastases are hematogenous, often to the lung

Question 17

Characteristics of undifferentiated pleomorphic sarcoma

Answer 17

Previously known as malignant fibrous histiocytoma

Large multilobulated tumor seen in the extremities and retroperitoneum of older adults

Microscopically they may have a storiform (cartwheel-like) pattern.

They recur and metastasize

Question 18

Characteristics of rhabdomyoma

Answer 18

Sarcoma botryoides

Affects infants and young children (age<5), in hwom it can cause a polypoid, “grapelike”, soft tissue mass that protrudes from the vagina

Question 19

Characteristics of embryonal rhabdomyosarcoma

Answer 19

Benign skeletal muscle tumor that can involve the vagina.

It occurs in middle-aged women

Question 20

Characteristics of leiomyoma

Answer 20

Benign smooth muscle tumor most often seen in the uterus and GI tract.

Less often it is seen in skin, and only rarely in deep soft tissue

Question 21

Characteristics of leiomyosarcoma

Answer 21

Soft tissue is less common than its counterpart in the GI tract and uterus.

In soft tissue is usually arises in the retroperitoneum of older women

Grossly the tumor is fleshy and white with hemorrhage and necrosis.

Microscopically the the tumor nuclei are blunt ended (“cigar shaped”). Longitudinal striations can be seen with Masson trichrome staining. The tumor is highly aggressive in the retroperitoneum

Question 22

Characteristics of botulism

Answer 22

Caused by exposure to a neurotoxin produced by Clostridium botulinum

Mechanism of action of the neurotoxin- blocks the release of acetylcholine from presynaptic neurons

Question 23

Characteristics of toxic myopathy

Answer 23

Caused by corticosteroid use
ICU
Chloroquine and hydroxychloroquine
Alcohol
Hypothyroidism

Question 24

Characteristics of myotonic dystrophy

Answer 24

AD multisystem disorder

Expanisions of CTG triplet repeats in the 3’-noncoding region of the myotonic dystrophy protein kinase (DMPK) gene on chromosome 19

Selective atrophy of type I fibers

Clinical features:
Muscle weakness and wasting
Myotonia (prolonged muscle contractions)
Cataracts
Frontal balding
Testicular atrophy
Arrhythmias

Question 25

Characteristics of malignant hyperthemia

Answer 25

Mutations in the RYR1 gene

Disrupt the function of the ryanodine receptor

Clinical features:
Tachycardia
Tachypnea
Muscle spasms
Hyperpyrexia
Rhabdomyolysis

Question 26

Characteristics of fibromyalgia

Answer 26

Syndrome characterized by widespread MSK pain without evidence of muscle inflammation or increase in muscle enzymes

Clinical features:
Fatigue and sleep disruption (easily fatigued, unrefreshed sleep)
Psychiatric (anxiety, depression)
Somatic symptoms (headache)
Cognitive disturbance (learning, memory, perception and problem solving)
Muliple, symmetric tender spots over joints, muscle, tendons

Question 27

Characteristics of polymyalgia rheumatica

Answer 27

Muscle pain and stiffness in the neck, shoulder, and pelvic girdle

Worse in the mroning and with activity

Known association with giant cell (temporal) arteritis

Question 28

Characteristics of psoas abscess

Answer 28

Causes:
Fever, back/flank pain, inguinal mass, difficulty walking

Pain referred to hip or knee

Pain exacerbated by movements that cause the psoas to be stretched to extended, such as hip extension