MSK Disorders

Muscular Dystrophies

Inherited disease > progressive degeneration > muscular dysfunction & necrosis

Classified; on inheritance pattern, clinical presentation & genes responsible

1. Duchenne Dystrophy; X-linked, mutation of dystrophin gene

Clinical features; early onsent, weakness, elevated serum creatine kinase levels, pseudohypertrophy of calf (fibrous & fatty tissue)

Diagnosis; immunostainig of dystrophin or genetic testing

Prognosis; very poor (due to resp. & cardiac difficulties)

2. Becker Dystrophy; X-linked, partial dystrophin deficit

3. Myotonic Dystrophy; autosomal dominant, affects chromosome 19, most common inherited muscle disease

Clinical features; apparent in adolescences, facial weakness & distal limb weakness, cataracts, frontal baldness, low intelligence, cardiomyopathy

Muscular Disorders

Myopathies

Non-examinable

Neurogenic Disorders

Spinal Muscular Atrophy

Degeneration of anterior horn cells > no innervation > muscle atrophy

1. Progressive infantile SMA (Werdnig-Hoffman disease); autosomal recessive, affects chromosome 5, present in babies, floppy, hypotonia, poor prognosis (<1 year)

2. Chronic childhood SMA; more intermediated form > longer survival, only pallative care available

Myasthenia Gravis

Due to autoantibodies vs ACh receptor cells > weakness, ptosis & dysphagia, associated with thymus gland disease > produce antigenic T cells

Rhambdomyolysis

Presents as diffuse lytic destruction of tissue, associated with viral infection/autoimmune damage, strenuous exercise, enzymatic/metabolic effects

Acute; sarcoplasmic content release > myoglobuninaemia & myoglobinuria > acute liver failure, lung/liver/brain damage

Chronic; alcohol intoxication or acute progression > toxin mediated destruction of muscle

Degenerative Disorders

Metabolic Bone Disorders

Osteoporosis

Most common disorder

Presents as slowly progressive bone erosion & reduced bone formation, cortical/trabeculae thinning & reduced number > reduced bone mass > less mass > less dense > prone to fracture

Localised; immobolised, paralysed limbs, malignant bone tumours & RA > due to reduced mobility/activity

Generalised; involves multiple aspects

Presents with; back pain, loss of height, kyphosis, 'compression fx'

Diagnosis; imaging, Calcium blood levels, urine calcium levels

Treatment; oestrogen/androgen therapy, increased dietary calcium, increased vit. C/D, exercise

Osteomalacia

Normal bone deposition but abnormal ostoid formed (incorrectly mineralised > weak)

Aetiology; vitamin D deficiency > vit. D absorption failure > hypocalaemia = bone resportion & reduced renal calcium excretion

Deficiency due to reduced diet intake, skin synthesis, malabsorption or renal disease

S/s; bone pain (microfractures), looser's zones (bone splitting), leg bowing

Rickets = osteomalacia in children > bowing/deformity of long bones, skull bone distortion & costochondral junction enlargement

Treatment; oestrogen therapy, balanced diet, exercise

Paget's Disease

Continuous destruction & replacement of bone with poorly mineralised matrix

Pathogenesis; osteoclasts > bone destruction > inadequate osteoblast activity > weak new bone

Forms; Polyostotic (affects many bones), monostotic (affects one bone or single potion)

Phases; osteolytic (intense bone resorption > vascularised CT & osteolysis), mixed (osteolysis & osteoblastic activity > random pattern of bone), Sclerotic (osteoblastic activty predominates > irregular thickened, spongy, soft bone)

S/s; pain, deformity, skull enlargement, platybasia, kyphosis & osteosarcoma, increased cardiac output > cardiomegaly

Treatment; with calcitonin (increased calcium blood absorption) & disphosphonates (osteoclast apoptosis)

Hyperparathyroidims

Elevated parathyroid hormone > activation of osteoclasts > increase plasma calcium levels

Clinical features; osteolytic lesions > brown tumours (due to haemosiderin deposits

Multiple brown tumours = Von Recklinghausen's disease of bone or Osteitis fibrosa cystica

Primary; = neoplasia & hyperplasia of thyroid > brown tumours likely

Secondary; = prolonged calcium deficiency > PTH stimulation > bone calcium release

S/s; renal calculi, depression, GIT anomalies

Treatment; brown tumour removal, correct dietary factors

Bone Infection Disorders

Osteomyelitis

Commonly affects cortex, medulla & periosteum

Aetiology; pyogenic bacteria

Direct access (environmental exposure) or bloodborne (bacteraemia) = most common

Clinical features; suppuration & bone destruction

Acute; acute purulent exudate in marrow cavity > trabeculae necrosis > may protrude skin surface > discharging sinus

Chronic; progression of acute or TB > bone destruction, fibrosis & focal suppuration > periosteum bone formation > abnormally shaped bone

Treatment; antibiotics & surgery

Bone Tumours

Benign Tumours

1. Osteoid osteoma; most common bone-forming tumour

Pathogenesis; osteoblasts producing irregular osteoid collagen > poorly mineralised bone

Clinical features; central dense lesion with halo of bone lucency around > gradual onset of deep aching pain, more severe at night

Types; Giant osteoid osteoma (larger - affects hands, feet & vertebrae), Ivory (densely compact bone with haversian systems - affects skull)

2. Chondroma; most common cartilage-forming tumour

Presents with a chondrocyte & cartilaginous matrix

Types; Enchondroma (single lesion), enchondromatosis (multiple lesion, premalignant)

3. Giant-cell tumour (osteoclastoma); Osteolytic tumour (may be benign or malignant)

Clinical features; effects knee, lower/upper femur, lower radius/sacrum

Histology; cells resemble large osteoclasts, highly vascular & may erode cortical bone

Prognosis; 10% 5yr s/r

Metastatic Tumours

1. Metastatic carcinoma; secondary from bronchus, breast, prostate, thyroid, stomach & kidney

Clinical features; multiple nodules, may be osteolytic/osteosclerotic

Symptoms; bone weakness, pain, fx., anaemia, kidney stones, depression, constipation, spinal nerve compression

2. Multiple Myeloma (Plasmacytoma); malignancy of plasma cells

Aetiology; prolonged antigenic stimulus w/ plasma cells

Pattern types; 1. diffuse plasma cell infiltration of marrow 2. Solitary osteolytic bone lesion 3. Multiple osteolytic lesions

Pathogenesis; highly vascular/cellular nodules > bone erosion > pain, fx., haematogenous spread, weight loss & fatigue

Prognosis; >90% 3yr s/r

3. Osteosarcoma; malignancy of osteoblasts

Clinical features; affecting knee region > pain, swelling, fx., weight loss & fever

Diagnosis; Codman's sign

Chondrosarcoma; malignancy of chondrocytes

Clinical features; well-differentiated on radiograph (glistening-white appearance)

Treatment; possible amputation due to high recurrence

4. Ewing's sarcoma; genetic abnormalities > malignancy

Clinical feature; peripheral primitive neuroectodermal tumour (derived from embryonic cells) > small undifferentiated spindle cells > in medullary cavity > destroys trabecular bone/erodes cortical bone > periosteum thickening > pain