## Diagnostic Approach to Bipolar I Disorder **Key Point:** Bipolar I disorder is a clinical diagnosis based on DSM-5 criteria; no single pathognomonic investigation confirms it. However, investigations are essential to exclude medical and secondary causes of mania. ### Why Thyroid and Calcium Assessment? **High-Yield:** Thyroid dysfunction (particularly hyperthyroidism) and hypercalcemia are the most common metabolic causes of secondary mania. These must be ruled out before attributing mood elevation to primary bipolar disorder. | Condition | Mechanism | Investigation | |-----------|-----------|----------------| | Hyperthyroidism | Excess thyroid hormone → sympathomimetic state, mimics mania | TSH (↓), free T4 (↑) | | Hypercalcemia | Neuropsychiatric effects via altered neurotransmission | Serum calcium, PTH, vitamin D | | Hypothyroidism | Can precipitate depression; important to exclude | TSH (↑), free T4 (↓) | **Clinical Pearl:** In the Indian context, iodine deficiency and autoimmune thyroiditis are common; thyroid screening is standard in all mood disorder presentations. ### Diagnostic Workup Algorithm ```mermaid flowchart TD A[Suspected Bipolar I: Mania + History of Depression]:::outcome A --> B[Clinical assessment for DSM-5 criteria]:::action B --> C{Exclude secondary causes?}:::decision C -->|Yes| D[TSH, free T4, serum calcium]:::action C -->|No| E[Proceed to psychiatric diagnosis] D --> F{Any abnormality?}:::decision F -->|Yes| G[Treat underlying medical condition]:::action F -->|No| H[Confirm Bipolar I Disorder]:::outcome H --> I[Initiate mood stabilizer]:::action ``` **Key Point:** This patient meets criteria for Bipolar I (at least one manic episode lasting ≥7 days + previous depressive episode). The investigation of choice is to rule out medical mimics, not to confirm the psychiatric diagnosis itself.
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