Differentiating Knee Conditions: A Case-Based Approach

A patient presents with a red, tender, and inflamed knee. The differential diagnosis includes prepatellar bursitis, osteoarthritis, localised cellulitis, rheumatoid arthritis, and gout.

prepatellar bursitis, also known as housemaid’s knee, carpet layer’s knee, or nun’s knee, is often caused by repetitive knee trauma. Treatment involves non-steroidal anti-inflammatory agents and local corticosteroid injection. Septic bursitis requires appropriate antibiotic cover and drainage.

Osteoarthritis is a diagnosis of exclusion and does not typically cause a red, tender, inflamed knee. Knee aspirate in this case would not show white cells.

Localised cellulitis may result in erythema but is unlikely to cause knee swelling. Knee aspirate in this case would not show white cells.

Rheumatoid arthritis is unlikely to present in men of this age and typically affects small joints of the fingers, thumbs, wrists, feet, and ankles.

Gout can be diagnosed through the presence of negatively birefringent crystals seen on joint microscopy.

In conclusion, a thorough evaluation of the patient’s symptoms and appropriate diagnostic tests are necessary to differentiate between these knee conditions.

After a diarrhoeal illness, the patient may be at risk of developing reactive arthritis, which is a possible diagnosis for both sacroiliitis and plantar fasciitis. However, it is less likely to be related to inflammatory bowel disease (IBD) if there is only one acute episode of diarrhoea.

Sacroiliitis is a condition that affects the sacroiliac joint, which is located at the base of the spine where it connects to the pelvis. It causes inflammation and pain in the lower back, buttocks, and legs. Plantar fasciitis, on the other hand, is a condition that affects the plantar fascia, a thick band of tissue that runs along the bottom of the foot. It causes pain and stiffness in the heel and arch of the foot.

Differentiating Arthritis Types: Avascular Necrosis, Gout, Osteoarthritis, Pseudogout, and Septic Arthritis

Arthritis is a common condition that affects the joints, causing pain, stiffness, and inflammation. However, there are different types of arthritis, each with its own causes, symptoms, and treatments. Here are some key points to differentiate between avascular necrosis, gout, osteoarthritis, pseudogout, and septic arthritis:

Avascular necrosis is a condition where the bone tissue dies due to a lack of blood supply. It can be caused by corticosteroid use, malignancy, or trauma. Femoral head collapse is a classic radiographic change in avascular necrosis.

Gout is a type of crystal arthritis that usually affects peripheral joints, such as the big toe, ankle, or knee. It is caused by the buildup of uric acid crystals in the joint, leading to sudden attacks of pain, redness, and swelling.

Osteoarthritis is a degenerative joint disease that occurs when the cartilage that cushions the joints wears down over time. It is more common in older adults and can affect any joint, but femoral head collapse does not occur in osteoarthritis.

Pseudogout is another type of crystal arthritis that usually affects peripheral joints. It is caused by the buildup of calcium pyrophosphate crystals in the joint, leading to similar symptoms as gout.

Septic arthritis is a bacterial infection of the joint that can cause severe pain, swelling, and fever. It is a medical emergency and requires prompt treatment with antibiotics. While septic arthritis should always be considered in a monoarthritis, it is less likely in cases where there are classic radiographic changes of avascular necrosis, risk factors, and a normal CRP without history of fever.

Acid-Base Disorders and Differential Diagnosis of Granulomatosis with Polyangiitis

In cases of metabolic acidosis with respiratory compensation, the primary issue is a decrease in bicarbonate levels and pH, which is accompanied by a compensatory decrease in pCO2. On the other hand, respiratory acidosis with metabolic compensation is characterized by an increase in pCO2 and a decrease in pH, which is accompanied by a compensatory increase in bicarbonate levels.

When nosebleeds are present, the diagnosis of Granulomatosis with polyangiitis is more likely than microscopic polyarteritis due to upper respiratory tract involvement. Goodpasture’s disease is less likely because it does not cause a rash. In particular, 95% of patients with Granulomatosis with polyangiitis develop antineutrophil cytoplasmic antibodies (cytoplasmic pattern) or cANCAs, with proteinase-3 being the major c-ANCA antigen. Conversely, perinuclear or p-ANCAs are directed against myeloperoxidase, are non-specific, and are detected in various autoimmune disorders.

Polymyalgia Rheumatica/Temporal arthritis: Symptoms and Treatment

Polymyalgia rheumatica/temporal arthritis is a condition that can cause a variety of symptoms. It may present with predominantly polymyalgia symptoms such as muscle pain and stiffness, or arthritis symptoms such as headaches, scalp tenderness, and jaw claudication. Systemic features like fever, malaise, and weight loss may also be present. Weakness is not a typical feature, but it may be apparent due to pain or stiffness with weight loss. The ESR (erythrocyte sedimentation rate) is usually very high in this condition.

Temporal arthritis is a serious complication of this condition that can result in blindness. It is important to note that temporal arthritis is a vasculitis that affects medium and large-sized arteries throughout the body, not just the temporal artery. The superficial temporal artery supplies the orbit of the eye and is a branch of the external carotid artery, while the ophthalmic artery supplies the majority of the blood to the eye itself and is a branch of the internal carotid artery. Inflammation and narrowing of the temporal artery can cause blindness.

If temporal arthritis is suspected, it must be treated with high-dose steroids. This condition is a reminder that prompt diagnosis and treatment are crucial to prevent serious complications.

The symptoms described suggest a diagnosis of ankylosing spondylitis, a chronic form of seronegative spondyloarthropathy that primarily affects the axial skeleton. Diagnosis is made using the modified New York criteria, which includes clinical and radiological criteria. HLA-B27 and sacroiliitis on MRI play a major role in the recently proposed ASAS diagnostic algorithm. Radiographic sacroiliitis is required for eligibility for anti-TNF treatment. Other conditions, such as pseudogout, Lyme disease, osteoarthritis, and rheumatoid arthritis, are unlikely diagnoses. Timely diagnosis requires a high index of suspicion.

Sites of Crystal Deposition in Pseudogout

Pseudogout is a condition characterized by the deposition of calcium pyrophosphate dihydrate (CPPD) crystals in various tissues of the body. The most common site of deposition is the synovial fluid, which can lead to joint inflammation and pain. However, CPPD crystals can also be deposited in other tissues such as cartilage, ligaments, tendons, and bursae.

Cartilage is another common site for CPPD crystal deposition, and pseudogout is also known as chondrocalcinosis. Deposition in the ligaments and tendons is possible but less common than in the synovium. Bursae deposition is also possible but less common than synovium deposition.

In summary, while CPPD crystals can be deposited in various tissues in pseudogout, the synovium is the most common site of deposition, followed by cartilage, ligaments, tendons, and bursae.

Differentiating Autoantibodies in Connective Tissue Diseases

Connective tissue diseases are a group of autoimmune disorders that affect various parts of the body. Differentiating between these diseases can be challenging, but autoantibodies can provide valuable clues. Here are some common autoantibodies and the connective tissue diseases they are associated with:

1. Anti-centromere antibody: This antibody is most likely to be present in limited systemic sclerosis (CREST).

2. Anti-Scl-70: This antibody is found in diffuse systemic sclerosis.

3. Anti-RNP antibody: This antibody is found in mixed connective tissue disease.

4. Anti-Ro antibody: This antibody is classically positive in Sjögren’s syndrome or systemic lupus erythematosus.

5. Anti-Jo-1 antibody: This antibody is commonly raised in polymyositis.

By identifying the specific autoantibodies present in a patient, healthcare providers can better diagnose and manage connective tissue diseases.

Systemic lupus erythematosus (SLE) is an autoimmune disease that primarily affects young women. It is caused by the deposition of immune complexes and can have a wide range of clinical effects, including a butterfly-shaped rash on the cheeks and nose, joint pain, and involvement of multiple organ systems such as the kidneys, lungs, and heart. SLE is associated with the presence of ANA and dsDNA antibodies, as well as low levels of C3 and C4 in the blood.

Mixed connective tissue disease (MCTD) is a syndrome that shares features with several other rheumatological conditions, including SLE, scleroderma, myositis, and rheumatoid arthritis. Common symptoms include fatigue, joint pain, pulmonary involvement, and Raynaud’s phenomenon. MCTD is strongly associated with anti-RNP antibodies.

Rheumatoid arthritis is an inflammatory arthritis that typically affects middle-aged women and causes symmetrical joint pain and stiffness, particularly in the hands and feet. If left untreated, it can lead to deformities that affect function. Rheumatoid arthritis is associated with the presence of autoantibodies such as rheumatoid factor and anti-CCP.

Polymyositis is an autoimmune myositis that causes weakness and loss of muscle mass, particularly in the proximal muscles. Other symptoms may include malaise and difficulty swallowing. Polymyositis is associated with anti-Jo1 autoantibodies.

Systemic sclerosis, also known as diffuse scleroderma, is an autoimmune disease that primarily affects women aged 30-50. It causes collagen accumulation, leading to thickening of the skin and vasculitis affecting small arteries. Systemic sclerosis can affect multiple organ systems, including the skin, lungs, kidneys, and gastrointestinal tract. It is associated with anti-Scl70 antibodies.

Septic Arthritis: Causes and Treatment

Septic arthritis is a rheumatological emergency that requires urgent attention. A red, hot, swollen joint may indicate septic arthritis, which can be caused by a variety of pathogens. The most common pathogen is Staphylococcus aureus, and joint destruction can occur within 24 hours if left untreated. It is important to consider and treat septic arthritis urgently or until firmly excluded by joint aspiration. The empirical antibiotic regime should be consulted in local health authority guidelines or with a microbiologist. Intravenous drugs should be used for 2 weeks and a total course of 6 weeks completed. Other pathogens that can cause septic arthritis include Neisseria gonorrhoeae, Mycobacterium tuberculosis, Streptococcus viridans, and Salmonella typhi. It is important to consider the patient’s medical history and risk factors when determining the cause of septic arthritis.