Muscle and Soft Tissue: Pathology

Myasthenia gravis (MG) is an autoimmune neuromuscular disorder characterized by weakness and fatigability of skeletal muscles caused by dysfunction/destruction of acetylcholine receptors at the neuromuscular junction. Myasthenia gravis presents with fatigue, ptosis, diplopia, dysphagia, respiratory difficulties, and progressive weakness in the limbs, leading to difficulty in movement. Diagnosis is established based on clinical presentation, detection of antibodies, and electrophysiologic studies. Management is aimed at increasing the activity of acetylcholine at the neuromuscular junction and suppression of antibodies. This disease can be associated with thymomas and thymic hyperplasia, and thymectomy is sometimes indicated. Myasthenia gravis can progress to a life-threatening cholinergic crisis with respiratory failure, but this is preventable with appropriate management. Prognosis is generally good with treatment, and some patients can achieve a long-term remission.

Duchenne muscular dystrophy (DMD) is an X-linked recessive genetic disorder that is caused by a mutation in the DMD gene. The mutation leads to the production of abnormal dystrophin, resulting in muscle-fiber destruction and replacement with fatty or fibrous tissue. Affected individuals present with progressive proximal muscle weakness leading to the eventual loss of ambulation, as well as contractures, scoliosis, cardiomyopathy, and respiratory failure. A marked elevation in CK may be observed. Genetic testing is used to confirm the diagnosis. Management is supportive and aimed at slowing disease progression and complications. Duchenne muscular dystrophy is fatal with a life expectancy of about 20 years of age.

A lipoma is a benign neoplasm of fat cells (adipocytes) and the most common soft tissue tumor in adults. The etiology is unknown, but obesity is a predisposing factor; genetics also play a role, with multiple lipomas occurring in various inherited disorders. Lipomas can arise in any site with adipose tissue (including the gastrointestinal tract, chest cavity, retroperitoneum, and glands), but are most common in subcutaneous tissues of the trunk or proximal extremities. The treatment is not necessary for small asymptomatic lipomas. Surgical excision is the treatment if there is a cosmetic, functional, or diagnostic concern.