Differential Diagnosis

The patient's symptoms of tightness in the Achilles, anterior tibialis tendon, and extensor hallucis tendon, which are abated by rest, along with weakness on resistance dorsiflexion of the left foot, and specific blood test results, guide the differential diagnosis. The blood test results showing low MCV (Mean Corpuscular Volume), MCH (Mean Corpuscular Hemoglobin), MCHC (Mean Corpuscular Hemoglobin Concentration), high triglyceride, cholesterol, RBC (Red Blood Cell) count, and lymphocytes, provide crucial clues.

• Single Most Likely Diagnosis

  • Chronic Lead Poisoning: This condition can cause a range of symptoms including muscle weakness, particularly affecting the extensor muscles of the hands and feet, which could explain the dorsiflexion weakness. Lead poisoning also leads to anemia characterized by low MCV, MCH, and MCHC, due to its effect on heme synthesis. The high RBC count might seem counterintuitive but can occur in the setting of chronic disease or as a response to anemia. Lead exposure is also associated with increased levels of triglycerides and cholesterol.

• Other Likely Diagnoses

  • Vitamin D Deficiency: Can lead to muscle weakness and bone pain. Although it doesn't directly explain the hematological findings, it's a common condition that can contribute to muscle symptoms.
  • Hypothyroidism: Can cause muscle weakness, elevated cholesterol and triglycerides, and sometimes anemia. However, the specific pattern of anemia and the presence of high RBC and lymphocyte counts are less typical.
  • Diabetic Neuropathy: Diabetes can cause neuropathy leading to weakness, particularly in the feet, and is associated with high triglycerides and cholesterol. However, the specific tendon involvement and hematologic abnormalities are not directly explained by diabetes alone.

• Do Not Miss Diagnoses

  • Amyloidosis: A condition where abnormal proteins (amyloid) accumulate in organs and tissues, potentially causing muscle weakness, neuropathy, and anemia. It's crucial to consider due to its potential for multi-organ involvement and the need for early diagnosis.
  • Multiple Myeloma: A plasma cell disorder that can cause anemia, bone pain, and elevated blood fats. Although less likely, it's a critical diagnosis not to miss due to its severity and the need for specific treatment.
  • Lymphoproliferative Disorders: Conditions like lymphoma can cause a wide range of symptoms including anemia, elevated lymphocyte count, and potentially muscle weakness due to neuropathy or direct muscle involvement.

• Rare Diagnoses

  • Porphyrias: A group of disorders that can lead to neurological symptoms including muscle weakness, and some forms can cause anemia and abnormal heme synthesis, potentially explaining the low MCV, MCH, and MCHC.
  • Mitochondrial Myopathies: A group of conditions that affect the mitochondria, leading to muscle weakness and potentially other systemic symptoms. They might not directly explain all the blood abnormalities but could contribute to the muscle symptoms.