Differential Diagnosis for Progressive Right Arm Weakness and Sensory Changes
Single Most Likely Diagnosis
- Radiation-Induced Brachial Plexopathy: This condition is a well-known complication of radiation therapy, particularly when the radiation field includes the brachial plexus, as might be the case with radiation to the supraclavicular lymph nodes. The delay of 7 years between radiation and symptom onset is within the expected timeframe, as radiation-induced brachial plexopathy can occur anywhere from a few months to many years after radiation exposure. The involvement of muscles like the trapezius, deltoid, biceps, and the presence of sensory changes are consistent with this diagnosis.
Other Likely Diagnoses
- Metastatic Disease Involving the Brachial Plexus: Given the patient's history of cancer (base of tongue and supraclavicular lymph node involvement), there is a possibility of metastatic disease affecting the brachial plexus. This could explain the progressive weakness and sensory changes, although the timeframe might be slightly longer than typically expected for some metastatic processes.
- Recurrent Primary Tumor: Recurrence of the primary tumor at the base of the tongue or in the supraclavicular lymph nodes could potentially compress or invade the brachial plexus, leading to the observed symptoms.
Do Not Miss Diagnoses
- Pancoast Tumor: Although less likely given the history of radiation and the specific pattern of weakness, a Pancoast tumor (a type of lung cancer located at the apex of the lung) could cause similar symptoms by compressing the brachial plexus. Missing this diagnosis could have significant implications for treatment and prognosis.
- Vascular Causes (e.g., Subclavian Artery Thrombosis or Embolism): Vascular events affecting the subclavian artery could lead to arm weakness and sensory changes due to decreased blood flow. While less directly related to the radiation history, these conditions are critical to identify due to their potential for acute intervention.
Rare Diagnoses
- Idiopathic Brachial Plexitis (Neuralgic Amyotrophy): This is an inflammatory condition of the brachial plexus that can cause sudden onset of pain, weakness, and atrophy of the muscles supplied by the affected nerves. While it doesn't directly relate to the radiation history, it's a rare condition that could present with similar symptoms.
- Hereditary Neuropathies (e.g., Charcot-Marie-Tooth Disease): These are genetic disorders that affect the peripheral nerves, potentially causing progressive weakness and sensory changes. However, the pattern of involvement and the late onset in relation to radiation therapy make this a less likely consideration in this context.