For many people living with more than one long-term illness, getting an accurate diagnosis can be a frustrating and lengthy journey. Symptoms often overlap, evolve over time, or resemble those of entirely different conditions, making it difficult for doctors to identify the full picture during a single consultation. As a result, patients may spend years moving between specialists before receiving the correct diagnosis and treatment plan. Experts say the challenge lies not only in the complexity of individual diseases but also in how multiple conditions interact with one another. According to the Longitudinal Ageing Study in India, published in BMJ Open, 27.39% of older Indian adults live with multiple chronic conditions. Globally, a landmark Lancet study analysing health records of 1.75 million people found that 23.2% had two or more chronic diseases, with multimorbidity affecting the majority of people aged 65 years and older. Meanwhile, a report published in BMJ Quality & Safety estimated that diagnostic errors may affect around 5% of adults receiving outpatient care each year, highlighting how challenging diagnosis can be.

Why Are Multiple Chronic Conditions So Difficult To Diagnose?

According to Dr. Sanjay Raina, Head, Department of Internal Medicine, Amrita Hospital, Faridabad, diagnosing multiple chronic conditions also known as multimorbidity is rarely straightforward because symptoms are seldom limited to one disease.

"Fatigue can be caused by anaemia, thyroid disorders, diabetes, heart disease, chronic inflammation, or even medicines taken for another illness. These overlaps can lead to multiple diagnoses that individually make sense, but the larger clinical pattern is not immediately evident," says Dr Raina. 

For example, a person experiencing tiredness, breathlessness, and weight changes may simultaneously have diabetes, thyroid disease, and heart disease, with each condition contributing to the same symptoms.

What Is Multimorbidity?

"For example, persistent fatigue may be due to anemia, hypothyroidism, diabetes, heart failure, depression, or even an autoimmune disorder. Similarly, joint pain could result from osteoarthritis, rheumatoid arthritis, vitamin D deficiency, or lupus. If we focus on just one symptom or one disease, we may overlook another underlying condition. Another challenge is that one illness can mask or worsen another. Diabetes can damage nerves, making heart disease symptoms less obvious. Long-term medications, such as steroids, can also produce side effects that resemble new diseases. In elderly patients especially, multiple medications (polypharmacy) may lead to confusion, dizziness, or fatigue, further complicating the diagnosis," explains Dr. Pramila Ramnis Baitha, Director Internal Medicine, Fortis Hospital, Greater Noida. Multimorbidity refers to the presence of two or more chronic medical conditions in the same person. These may include combinations such as:

  • Diabetes and hypertension
  • Heart disease and chronic kidney disease
  • Arthritis and osteoporosis
  • Thyroid disorders and anaemia
  • Chronic lung disease and heart failure

Managing these conditions together is often far more complicated than treating a single illness.

Why Symptoms Often Overlap

Many chronic illnesses share common symptoms, including:

  • Fatigue
  • Weight changes
  • Body aches
  • Shortness of breath
  • Poor concentration
  • Sleep disturbances

These overlapping symptoms can make it difficult to determine whether a new complaint represents:

  • A completely new illness
  • Progression of an existing disease
  • Side effects of medication
  • Interaction between multiple conditions

More Tests Are Not Always The Solution

Many people assume additional scans or blood tests automatically lead to faster diagnosis. However, Dr. Raina says that indiscriminate testing alone is rarely the answer. Instead, doctors often need to carefully review:

  • Previous medical records
  • Medication history
  • The sequence in which symptoms developed
  • Existing chronic illnesses
  • Lifestyle and family history

Continuity of care seeing the same healthcare team over time also plays an important role in recognising patterns that may otherwise be missed.

Why A Holistic Approach Matters

Experts believe modern medicine increasingly needs to move beyond treating each disease in isolation. As Dr. Raina explains, "Medicine has to change from a conception of diseases as separate entities to understanding the patient as one interconnected biological system. That approach improves the diagnosis of complex conditions." Rather than focusing only on individual diseases, doctors are increasingly looking at how different organs, medications, and health conditions influence one another.

What Patients Can Do

If you have several ongoing health problems, experts recommend:

  • Keeping a record of all your symptoms
  • Carrying an updated list of medications
  • Informing every doctor about all existing medical conditions
  • Attending regular follow-up appointments
  • Reporting any new or changing symptoms promptly
  • Avoiding self-medication without medical advice

Maintaining continuity with one primary physician can also help coordinate care between different specialists. Diagnosing multiple chronic conditions is rarely simple because many illnesses share similar symptoms and often coexist. Fatigue, pain, breathlessness, or weight changes may have several underlying causes rather than just one. Instead of relying solely on more investigations, experts say careful clinical evaluation, continuity of care, medication review, and understanding how diseases interact are key to reaching the correct diagnosis. Recognising the patient as a whole not just a collection of separate illnesses can ultimately lead to better treatment and improved long-term health outcomes.



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