Musculoskeletal Pathology USMLE

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OSTEOPOROSIS ("Porous Bones") Definition: WHO: Bone Mineral Density (BMD) $> -2.5$ SDs below mean BMD NB: Osteopenia: BMD between $-1.0$ & $-2.5$ SDs below mean BMD Etiology: Primary: Type 1: Postmenopausal Osteoporosis (vertebrae & NOF; females only) $\downarrow$ Estrogen $\to \uparrow$ Osteoclast Activity Type 2: Senile Osteoporosis (affects all bones; males & females) $\downarrow$ Synthetic/Replicative Ability of Osteoblasts $\to \downarrow$ Osteoblast Activity Secondary: Endocrine (Cushing's, $\uparrow$ PTH, Hyper/Hypothyroidism, DM, Acromegaly, Addison's) Pregnancy & Lactation Myeloma Malnutrition/Malabsorption Drugs ( Corticosteroids , Chemo, etc.) Alcohol, Immobility Pathogenesis: $\uparrow$ Osteoclast / $\downarrow$ Osteoblast Function Imbalance $\to \uparrow$ Bone Resorption $\to$ Porous Bones $\to \downarrow$ Bone Mass Morphology: Trabeculae are Thinner & Fewer than Normal Clinical Features: Symptoms: Often asymptomatic until fracture. Complications: "Fragility Fractures" (minimal trauma) NB: Rel-Risk DOUBLES with every 1.0 SD Deviation Below the Mean! $ Vertebral Compression Fracture $\to$ Spinal Cord Compression, Cauda Equina Syndrome Investigations: Plain X-Ray **DXA (Dual-energy X-ray Absorptiometry) Bone-Mineral-Density Scan: **ESSENTIAL: Lumbar Spine + Hip *OPTIONAL: Forearm Interpretation of T-Scores & Z-Scores: T-Score: Patient's BMD vs. Young-Normal BMD (Used for post-menopausal women) Z-Score: Patient's BMD vs. Age-Matched Mean BMD (Used for people $ + Ix for underlying cause: ESR (Exclude Myeloma), Vit.D Level (Exclude 2º Osteoporosis), PTH Level (Exclude Hyperparathyroidism), TSH Level (Exclude Hyperthyroidism) Treatment & Prevention: Pharmacological: **Bisphosphonates (e.g., Alendronate, Risedronate) - (Monthly Dose) Or Strontium $\to$ (Stimulates Ca-Deposition & Inhibits Bone Resorption) +/- Hormonal - ( SERMS (e.g., Raloxifene) or HRT (If Perimenopausal/Post-Menopausal)) OTC Supplements: (Calcium & Vit D) Occupational: (Reduce Falls Risk, $\uparrow$ Weight-Bearing Exercise) PAGET'S DISEASE OF THE BONE Etiology: Genetic Pathogenesis: Continuous Remodeling of Bone (Excess Turnover) $\to$ Weak, Deformed Bones & Arthritis Morphology: Markedly Thick, Deformed bones Clinical Features: May affect One or All bones Young-middle age Symptoms: Bone Pain, Arthritis Pathological Fractures (Thick Bones, but Fragile) Sclerosis, Deformity Nerve Compression, Deafness Diagnosis: X-Ray: Advancing Osteolytic Areas in Long Bones or Skull Compensatory Osteoblastic activity $\to$ Bone Thickening $\uparrow$ Alkaline Phosphatase Level (with normal Ca & PO4) Complications: Osteosarcoma Treatment: Bisphosphonates (Kills Osteoclasts) Calcitonin (Inhibits Osteoclast Activity) Prognosis: No Cure Good Prognosis if treated before major bone changes have occurred. POLYMYALGIA RHEUMATICA (PMR) Etiology: Unknown Association with Giant-Cell Arteritis (Temporal Arteritis - A Vasculitis) + Genetic (HLA-DR4) Susceptibility + Possible Viral Trigger (Parvovirus, Parainfluenza Virus, Adenovirus) Pathogenesis: Autoimmune Attack on the Joints & Muscles Clinical Features: Older Females ($2 \text{F}:1 \text{M}$, $>50$ yrs) Severe Symmetrical Myalgia (NOT Arthralgia) of Proximal Extremities (Shoulder/Pelvic Girdle) + Muscle Tenderness, BUT NO Weakness or Atrophy Myalgia Worst in Mornings + Constitutional Symptoms - (Fever, Weight Loss, Fatigue, Anorexia, Anemia, Malaise) Diagnosis: $>50$ yrs $>2$ Muscle Groups Affected Elevated ESR & CRP Responsive to Corticosteroids NB: NORMAL Creatinine Kinase Treatment: Corticosteroids RHEUMATOID (AKA: "Seropositive") ARTHRITIS Etiology: Genetic Autoimmune Pathogenesis: Genetic (HLA-DR4 & -DR1 Genes) $\to$ Rheumatoid Factor Production (Anti-IgG Ab) $\to$ Autoimmune $\to$ Macrophage-Mediated Local Joint Inflammation & Destruction Morphology: Erosion of the Articular Cartilage down to the bone. Pannus - Inflamed thickened hyperplastic synovium with papillary projections Fibrous Ankylosis (Bone Fusion) Clinical Features: Chronic, Multisymptom Condition Onset Age: $20-40$ yrs Symmetrical, POLY-arthritis, with Morning Stiffness. Particularly MCP & PIP Joints of the Hand "Morning Stiffness" - (As with all Inflammatory Arthroses) Joint Crepitus Signs: "Swan-Neck Deformity" – (Ulnar Deviation & Subluxation of the MCP Joints) Ankylosis (Fusion) & Restriction of movement $\to$ Muscle Wasting Dermatologic - Rheumatoid Nodules (e.g., Elbows) Vasculitis - Digital Infarcts (can cause gangrene) Ophthalmologic - Dry eyes, Scleritis Pulmonary - Fibrosis, lung nodules, pleuritis, effusion Cardiac - pericarditis, pericardial effusion, valvular defects, conduction defects GI - PUD (from NSAIDS), dry mouth Renal - Amyloidosis $\to$ Proteinuria Hepatic - Nodules (Nodular regenerative hyperplasia), portal fibrosis Neurologic - Cervical spine instability, peripheral nerve entrapment Haematologic - Lymphadenopathy, splenomegaly and leukopenia, amyloidosis, anaemia. Diagnosis: Diagnostic Criteria: (Requires $4^*$ of the Following Features for Diagnosis) Morning Stiffness $>3$ Joints MCP/PIP/Wrist Joints. Symmetrical Arthritis Rheumatoid Nodules in Skin RA Seropositivity (Rheumatoid Factor in Serum) X-Ray Changes: Erosions Lab: Old - Serum Rheumatoid Factor Positive (Anti-IgG IgM Antibodies) - Hence "Seropositive" New - ACCP - ("Anti-Cyclic Citrullinated Peptide Antibody Test) $95\%$ Specificity + Elevated ESR Treatment: DMARDS - ( Methotrexate, Sulfasalazine ) NSAIDS - For Symptomatic Control Corticosteroids: Short-term adjuvants. SEPTIC ARTHRITIS (Infection) Etiology: Joint Infection Common Bugs - N. gonorrhoeae, S. aureus , Other less commons. Pathogenesis: Routes of Spread - Hematogenous (Commonest), Direct from Adjacent Tissue, Iatrogenic. Clinical Features – A Medical Emergency! (If Gonococcal $\to$ Preceding Bacteremia with Maculopapulovesicular Skin Lesions & Migrating Polyarthritis $\to$ Settling into Monoarthritis - Typically Knee) Typically Severe Mono-Arthritis. (Joint often held in slight flexion to $\downarrow$ Pain) Swelling, Erythema, Hot, $\downarrow$ ROM due to Pain + Fever + Malaise (+/- Signs of Acute Sepsis – Fever, Chills, Dehydration, Lethargy) Diagnosis: Joint Aspirate + MCS. (Crystals?, Gram Stain?) FBC ($\uparrow$ WBC) $\uparrow$ ESR, CRP Endocervical/Urethral Swab or Urine PCR for Gonococcal. Treatment: If Gonococcal - Azithromycin, Ceftriaxone or Doxycycline If Staph - Ampicillin, Erythromycin or Vancomycin Analgesia Arthroscopy - Aspiration & Washout (+/- Surgical Debridement/Joint Replacement) (NB: DO NOT USE Intra-Articular Steroids!!) Complications: Avascular Necrosis of Femoral Head (if $\uparrow$ Intra-Articular Pressure due to Pus) Cartilage & Epiphyseal Destruction Osteomyelitis (Bone Infection) ANKYLOSING SPONDYLITIS ("Fusing Spinal Arthritis") Etiology: Genetic ( HLA-B27 ) Association $100\%$ Concordance in Identical Twins Pathogenesis: Enthesitis (Inflammation of Ligament Insertion Points on bone) (NB: In spine: $\to$ Ossification of Outer Fibers $\to$ Bridging Syndesmophytes $\to$ Fusion) Morphology: Syndesmophytes - (Bone formation between the intervertebral disks) Ankylosis Clinical Features: Young Males ($3 \text{M}:1 \text{F}$, Onset between $15-25$ yrs) Symptoms: Axial: Mid-Lower Back Pain + Stiffness Sacroiliitis $\to$ Persistent Buttock Pain Postural Changes ($\uparrow$ Kyphosis) Appendicular: Asymmetric Large-Joint Arthritis (Hips & Shoulder) + Morning Stiffness: Extra-Articular Manifestations: Ocular: Iritis, Anterior Uveitis Heart: Aortitis, Aortic Regurgitation, Pericarditis. Kidney: IgA Nephropathy & Amyloidosis Diagnosis: Clinical: $\uparrow$ Occiput-to-wall distance (Kyphosis) $\downarrow$ ROM of Spine Chest Wall Expansion Painful Sacroiliac Joint X-Ray: Sacroiliac Joint: "Pseudowidening" of joint due to Erosion Spine: "Squaring of Edges" of Vertebral Bodies from Erosion & Sclerosis $\to$ "Bamboo Spine" Treatment: DMARDS (Sulfasalazine/Methotrexate) for Peripheral Arthritis Infliximab (TNF$\alpha$-Inhibitors) $\to$ Treats underlying inflammation. NSAIDs (Symptomatic Only) Physio & Regular Exercise (Supportive Only) Surgery - (Hip Replacement / Vertebral Osteotomy) Prognosis: Morbidity (Due to Spinal Deformity), Not Mortality. REACTIVE ARTHRITIS (Eg. Enteropathic Arthritis & Reiter's Syndrome) = Any Arthritis FOLLOWING an INFECTION. (e.g., Rheumatic Fever, Reiter's Syndrome, etc) Etiology: Post-Infective - (Typically either GI or UTI): GI: Shigella, Salmonella, Campylobacter ( Enteropathic Arthritis ) UTI: Chlamydia ( Reiter's Syndrome ) + Genetic Susceptibility: HLA-B27 -Positive, Middle-Aged Males ($10 \text{M}:1 \text{F}$, $20-40$ yrs) Pathogenesis: Autoimmune Arthritis Initiated by Bacterial Infection Clinical Features: Onset: Within $1$ mth Post-Infection Duration: Typically Self-Limiting (Weeks-Years) Symptoms: Articular: Asymmetric, Peripheral Arthritis Extra-Articular: Iritis/Conjunctivitis, Urethritis/Cervicitis (if Chlamydia ). Mnemonic: "Can't see, can't pee, can't climb a tree" (Conjunctivitis, Urethritis, Arthritis) Diagnosis: Clinical Diagnosis Only Reiter's Clinical Triad – $1$. Arthritis, $2$. Conjunctivitis, $3$. Urethritis/Cervicitis. Lab Findings are Normal Cultures are Sterile Treatment: Antibiotics if Infection is Present NSAIDS Intra-Articular Steroid Injection Exercise PSORIATIC ARTHRITIS Etiology: Complication of Psoriasis (Unknown Etiology – but Genetic/Immunologic Association) Pathogenesis: Autoimmune T cells infiltrate the Skin & Joints $\to$ Inflammation Morphology: Plaque covered with Silvery Scales (Due to Hyperkeratosis & Parakeratosis), Oncholysis (Nail Pitting) Clinical Features: Primary Disease - Skin: Plaque covered with Silvery Scales (Due to Hyperkeratosis & Parakeratosis) Oncholysis (Nail Pitting) Multisystem Disorder: *Symmetric Arthritis of DIP Joints (Similar to RA) - (Seen in $30\%$ of Psoriasis Cases) + "Dactylitis" - (Sausage-Fingers & Sausage-Toes) + (Achilles Tendonitis) + (Plantar Fasciitis) Eye - Conjunctivitis & Iritis Treatment: DMARDS (Methotrexate / Sulfasalazine) Corticosteroids Moisturizers Phototherapy Prognosis: Lifelong Condition - No Cure.