Differential Diagnosis

Given the presentation of myopathy, tumor, and dysautonomia with normal bloodwork, including CK levels, the differential diagnosis can be organized into the following categories:

• Single Most Likely Diagnosis
  • Mitochondrial myopathy: This condition affects the mitochondria, the energy-producing structures within cells, and can present with myopathy, dysautonomia, and other systemic features without necessarily elevating CK levels. The normal bloodwork, including CK, does not rule out mitochondrial disorders, as they often have a more subtle biochemical presentation.
• Other Likely Diagnoses
  • Inclusion body myositis (IBM): Although CK levels can be normal in IBM, especially in the early stages or in some variants, the presence of myopathy and potential systemic symptoms like dysautonomia could suggest this diagnosis. However, IBM typically presents with slowly progressive weakness and may not fully account for the dysautonomia.
  • Paraneoplastic syndromes: These are conditions caused by the immune response to a tumor, but not due to direct local effects of the tumor cells. They can present with a wide range of symptoms, including myopathy and dysautonomia, before the tumor is identified. Normal bloodwork does not exclude this possibility, especially if the tumor is small or of a type that does not significantly alter common blood tests.
• Do Not Miss Diagnoses
  • Lambert-Eaton Myasthenic Syndrome (LEMS): This is an autoimmune disorder that can present with myopathy-like symptoms, dysautonomia, and is often associated with small cell lung cancer. It's crucial to consider LEMS because it is treatable and has a significant impact on prognosis if a tumor is present.
  • Multiple system atrophy (MSA): This is a rare neurodegenerative disorder that affects adult men and women, presenting with a combination of symptoms that include dysautonomia, parkinsonism, and cerebellar ataxia. Myopathy might not be a primary feature, but the presence of dysautonomia and potential for other systemic symptoms makes it a "do not miss" diagnosis due to its poor prognosis and the need for early supportive care.
• Rare Diagnoses
  • Dermatomyositis or polymyositis with normal CK: While these conditions typically present with elevated CK levels, there are cases where CK can be normal, especially in the early stages or in certain subsets of patients. The presence of skin manifestations (in dermatomyositis) or specific muscle biopsy findings could support this diagnosis.
  • Stiff person syndrome: This is a rare autoimmune disorder characterized by progressive stiffness and rigidity of the muscles, which could be mistaken for myopathy. It may also present with dysautonomia and can be associated with other autoimmune conditions or tumors.

Each of these diagnoses requires careful consideration of the clinical presentation, further diagnostic testing (such as muscle biopsy, imaging for tumors, and specific autoantibody tests), and potentially a trial of treatment to confirm the diagnosis and guide management.