Connective Tissue Disease – Top USMLE Diseases

Pneumonia is the infection of the lung parenchyma, resulting from the spread of pathogens and accompanied by the host inflammatory response. This condition is the most common infectious cause of death. Multiple organisms cause pneumonia, including bacteria (of which Streptococcus pneumoniae is the most common), viruses, and fungi. The infection can be acquired while hospitalized (hospital-acquired) or outside the hospital setting (community-acquired). Common symptoms include fever, chills, cough, chest pain, and dyspnea. Chest X-ray usually shows consolidation and/or infiltrates. Diagnosis can be made with clinical presentation and imaging, but in severe cases, microbiological testing (sputum and cultures, molecular testing) and routine blood tests are needed. Empiric treatment with antibiotics is recommended, with regimen depending on the setting, risk factors for multidrug-resistant organisms, and individual comorbidities. Identification of the causative pathogen helps narrow down the antibiotics. Preventive measures include vaccinations (pneumococcal and influenza) and smoking cessation.

Reactive arthritis is a seronegative autoimmune spondyloarthropathy that occurs in response to a previous gastrointestinal (GI) or genitourinary (GU) infection. The pathophysiology of this disease is unclear, but a significant proportion of affected patients are positive for HLA-B27. The disease manifests as asymmetric oligoarthritis (particularly of large joints in the lower extremities), enthesopathy, dactylitis, and/or sacroiliitis. Ocular, mucocutaneous, GI, GU, and cardiac manifestations may also occur. The diagnosis is clinical, and efforts should be made to rule out alternative diagnoses. Management focuses on controlling symptoms, typically with nonsteroidal anti-inflammatory drugs. An active infection, particularly Chlamydia trachomatis, should also be treated.

Psoriasis is a common T-cell–mediated inflammatory skin condition. The etiology is unknown, but is thought to be due to genetic inheritance and environmental triggers. There are 4 major subtypes, with the most common form being chronic plaque psoriasis. Plaques are well-circumscribed and salmon-colored, with silvery scales. Plaques commonly appear on the scalp and extensor surfaces of the extremities. Diagnosis is clinical. Treatment options are determined by the percentage of body surface area affected and include topical corticosteroids, retinoids, calcineurin inhibitors, disease-modifying antirheumatic drugs (DMARDs), biologics, and phototherapy.

Psoriasis is a common T-cell–mediated inflammatory skin condition. The etiology is unknown, but is thought to be due to genetic inheritance and environmental triggers. There are 4 major subtypes, with the most common form being chronic plaque psoriasis. Plaques are well-circumscribed and salmon-colored, with silvery scales. Plaques commonly appear on the scalp and extensor surfaces of the extremities. Diagnosis is clinical. Treatment options are determined by the percentage of body surface area (BSA) affected and include topical corticosteroids, retinoids, calcineurin inhibitors, disease-modifying antirheumatic drugs (DMARDs), biologics, and phototherapy.

Reactive arthritis is a seronegative autoimmune spondyloarthropathy that occurs in response to a previous gastrointestinal (GI) or genitourinary (GU) infection. The pathophysiology of this disease is unclear, but a significant proportion of affected patients are positive for HLA-B27. The disease manifests as asymmetric oligoarthritis (particularly of large joints in the lower extremities), enthesopathy, dactylitis, and/or sacroiliitis. Ocular, mucocutaneous, GI, GU, and cardiac manifestations may also occur. The diagnosis is clinical, and efforts should be made to rule out alternative diagnoses. Management focuses on controlling symptoms, typically with nonsteroidal anti-inflammatory drugs. An active infection should also be treated, particularly Chlamydia trachomatis.

Scleroderma (systemic sclerosis) is an autoimmune condition characterized by diffuse collagen deposition and fibrosis. The clinical presentation varies from limited skin involvement to diffuse involvement of internal organs. Diagnosis is established by a combination of physical findings and serology. There is no curative treatment. Management options are limited and include immunosuppressive medications as well as specific organ- or symptom-directed drugs. The overall 5-year survival of patients with scleroderma is about 80%.

Polymyositis (PM) is an autoimmune inflammatory myopathy caused by T cell-mediated muscle injury. The etiology of PM is unclear, but there are several genetic and environmental associations. Polymyositis is most common in middle-aged women and rarely affects children. Patients present with progressive and symmetric proximal muscle weakness and constitutional symptoms. Complications may arise from respiratory, cardiac, or GI involvement. Diagnosis is based on clinical presentation and laboratory studies and confirmed using muscle biopsy. Management is with systemic glucocorticoids, immunosuppressants, and physiotherapy. All patients should undergo cancer screening because there is a strong association with malignancy.

Dermatomyositis (DM) is an autoimmune and inflammatory myopathy. Although the etiology of DM is unclear, it has several genetic and environmental associations. Dermatomyositis is common in women around the age of 50 years. Patients present with symmetrical, proximal weakness, characteristic skin manifestations, and systemic symptoms. Diagnosis is based on clinical presentation and laboratory studies and confirmed on the basis of muscle biopsy. Myositis-specific antibodies, including anti-Mi-2, are specific markers in DM. Management is with systemic glucocorticoids, immunosuppressants, and physiotherapy. As there is a strong association of DM with malignancy, all patients should undergo cancer screening.

Pneumocystis jiroveci is a yeast-like fungus causing pneumocystis pneumonia (PCP) in immunocompromised patients. Pneumocystis pneumonia is spread through airborne transmission and classically affects patients with AIDS, functioning as an AIDS-defining illness. Patients may present with insidious onset of fever, chills, dry cough, chest pain, and shortness of breath. The diagnosis is supported by an increased β-D-glucan level and diffuse, bilateral infiltrates on chest imaging in the immunocompromised patient. A definitive diagnosis can be given with microscopy of induced sputum or specimens from bronchoalveolar lavage (BAL). Management involves antimicrobial therapy with a trimethoprim-sulfamethoxazole combination, and supportive care. Addressing the etiology of immunodeficiency is paramount. Prophylaxis is often required to prevent infection or reinfection.

Disease-modifying antirheumatic drugs are antiinflammatory medications used to manage rheumatoid arthritis. The medications slow, but do not cure, the progression of the disease. The medications are classified as either synthetic or biologic agents and each has unique mechanisms of action and side effects. Common side effects among the disease-modifying antirheumatic drugs include bone marrow suppression and hepatotoxicity. Leflunomide, methotrexate, and tumor necrosis factor (TNF)-ɑ inhibitors are avoided in pregnancy due to their potential teratogenicity. Hydroxychloroquine and sulfasalazine are safe for use during pregnancy.

Autoimmunity is a pathologic immune response toward self-antigens, resulting from a combination of factors: immunologic, genetic, and environmental. The immune system is equipped with self-tolerance, allowing immune cells such as T cells and B cells to recognize self-antigens and to not mount a reaction against them. Defects in this mechanism, along with environmental triggers (such as infections) and genetic susceptibility factors (most notable of which are the HLA genes) can lead to autoimmune diseases. These conditions are more commonly seen in women. Autoimmune diseases are chronic, with clinical manifestations consistent with the associated immune response. Among these conditions are Graves’ disease (autoantibodies against thyroid hormone receptors), myasthenia gravis (antibodies against acetylcholine receptors), type 1 diabetes (pancreatic β-cell destruction by immune cells), and systemic lupus erythematosus (multiorgan damage driven by immune complexes and autoantibodies).

Systemic lupus erythematosus (SLE) is a chronic autoimmune, inflammatory condition that causes immune-complex deposition in organs, resulting in systemic manifestations. Women, particularly those of African American descent, are more commonly affected. The clinical presentation can vary greatly. Notable clinical features include malar rash, nondestructive arthritis, lupus nephritis, serositis, cytopenia, thromboembolic disease, seizures, and/or psychosis. Diagnosis is based on clinical criteria, and includes tests to determine ANAs, SLE-specific antibodies, and specific clinical findings. The goal of management is to control symptoms and prevent organ damage, using corticosteroids, hydroxychloroquine, and immunosuppressants.

Rheumatoid arthritis (RA) is a symmetric, inflammatory polyarthritis and chronic, progressive, autoimmune disorder. Presentation occurs most commonly in middle-aged women with joint swelling, pain, and morning stiffness (often in the hands). Systemic inflammation can lead to extraarticular manifestations such as rheumatoid nodules, interstitial lung disease, Felty syndrome, and pericarditis. Prolonged and severe disease can lead to irreversible joint deformities. Diagnosis is based on strong clinical suspicion and confirmed by the presence of rheumatoid factor (RF), anti-cyclic citrullinated peptide (anti-CCP) antibodies, and characteristic imaging. Management involves long-term disease-modifying antirheumatic drugs (DMARDs), biologic agents, and physical therapy. Glucocorticoids and nonsteroidal antiinflammatory drugs (NSAIDs) are the treatment of choice for acute exacerbation.

Sjögren syndrome (SS) is an autoimmune, inflammatory condition where glandular tissues, such as the salivary and lacrimal glands, are infiltrated by lymphocytes, resulting in decreased tear and saliva production. The disease mainly affects middle-aged women, and is associated with other autoimmune conditions. Patients may experience symptoms and complications related to dry eyes and mouth. There is a wide range of extraglandular manifestations, including Raynaud's phenomenon, neuropathy, and cutaneous vasculitis. Patients are also at an increased risk of developing non-Hodgkin's lymphoma. Diagnosis is based on the presence of symptoms, and is validated by the clinical examination, serologic studies, or salivary gland biopsy. A multidisciplinary approach is needed to manage patients and targets symptomatic relief, with immunosuppressive therapy reserved for severe symptoms.

Pneumonia or pulmonary inflammation is an acute or chronic inflammation of lung tissue. Causes include infection with bacteria, viruses, or fungi. In more rare cases, pneumonia can also be caused through toxic triggers through inhalation of toxic substances, immunological processes, or in the course of radiotherapy.