Medical brain notes 15

  INFLAMMATORY MYOPATHIES   Polymyositis  is an autoimmune disease seen in adults. It presents with bilateral   proximal muscle weakness. Microscopic exam demonstrates endomysial lympho-cytic inflammation (mostly cytotoxic T8) and skeletal muscle fiber degeneration and regeneration. Patients respond to immunosuppression. Dermatomyositis   is a 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 demonstrates perimysial and vascular lymphocytic inflamma-tion, perifascicular fiber atrophy, and skeletal muscle fiber degeneration and regen-eration. Adult patients are at increased risk of lung, colon, breast, and gynecologic cancers. Inclusion body myositis  affects adults age >50, causing slowly progressive, asym-metrical, distal muscle weakness. Light microscopy ...

  MYASTHENIC SYNDROMES Myasthenia gravis  is an autoimmune disease characterized by autoantibodies   against the acetylcholine (ACh) receptor of the neuromuscular junction, resulting in muscular weakness predominantly affecting the facial muscles. Females are affected more frequently than males. •           Extraocular muscle weakness may lead to ptosis and diplopia; the weakness worsens with repeated contractions. •           Respiratory muscle involvement may lead to death. •           There is an association with thymic hyperplasia and thymomas. Treatment is anticholinesterase agents, steroids, and thymectomy. Lambert-Eaton myasthenic syndrome  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 a...

  MUSCULAR DYSTROPHY Duchenne muscular dystrophy  is a recessive X-linked form of muscular dystrophy   leading to rapid progression of muscle degeneration. It is the most common and severe form of muscular dystrophy. The affected gene is the dystrophin gene on the X chromosome (Xp21); dystrophin protein is an important muscle structural protein, and mutation results in a virtual absence of the dystrophin protein. Affected boys are normal at birth but have onset of symptoms by age 5. Clinical features include: •           Progressive muscular weakness •           Calf pseudohypertrophy •           Proximal weakness of shoulder and pelvic girdles •           Possible heart failure and arrhythmias •           Respiratory insufficiency and pulmonary infec...

  INFLAMMATORY NEUROPATHY Guillain-Barré syndrome is an autoimmune disease leading to the destruction of Schwann cells and peripheral nerve demyelination. Clinically, it is preceded by a viral illness. Muscular weakness occurs with an ascending paralysis, accompanied by loss of deep tendon reflexes. Diagnosis can be established with nerve conduction studies; lumbar puncture shows elevated protein. Microscopic examination demonstrates inflammation and demyelination of periph-eral nerves and spinal nerve roots, resulting in muscular weakness. Guillain-Barré syndrome is fatal in 5% of cases because of respiratory paralysis. Treatment is plas-mapheresis and immunoglobulin therapy.

  SOFT TISSUE AND PERIPHERAL NERVE TUMORS Lipoma  is a 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. The tumor is usually more of a cosmetic problem than a medical one. Microscopically, it is composed of mature fat cells but can contain other mesen-chymal elements. Liposarcoma  is a malignant adipose tissue tumor that most often arises in the thigh or retroperitoneum. It is the most common adult sarcoma. It is distinguished 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 mul-tivacuolated lipoblasts. Metastases are rare but retroperitoneal tumors tend to recur. Dermatofibroma  is a benign dermal spindle cell proliferation that most often arises in ...