**Patient Analysis: Headache in a 13-year-old Male**

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### 1. Potential Differential Diagnoses

Given the limited information, the following are common and important causes of headache in adolescents:

- **Primary Headache Disorders**
  - Migraine (with or without aura)
  - Tension-type headache
  - Cluster headache (less common in this age group)
- **Secondary Headache Causes**
  - Viral or bacterial infections (e.g., sinusitis, meningitis)
  - Medication overuse headache
  - Refractive errors (vision problems)
  - Trauma (concussion, subdural hematoma)
  - Intracranial mass or space-occupying lesion
  - Idiopathic intracranial hypertension
  - Hypertension
  - Dental or temporomandibular joint (TMJ) disorders

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### 2. Recommended Diagnostic Tests

**Initial Evaluation:**
- Detailed history (onset, duration, character, associated symptoms, triggers, family history)
- Physical examination (including neurological and fundoscopic exam)

**Based on findings, consider:**
- **Basic investigations:**
  - CBC, ESR/CRP (if infection or inflammation suspected)
  - Urinalysis (if systemic illness suspected)
- **Imaging:**
  - MRI or CT brain (if red flags present or abnormal neurological findings)
- **Other:**
  - Vision assessment (if visual symptoms)
  - Lumbar puncture (if meningitis or increased intracranial pressure suspected)

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### 3. Urgency Level

- **Low**: If headache is mild, intermittent, and not associated with red flags.
- **Medium**: If headache is moderate, persistent, or associated with mild systemic symptoms.
- **High**: If any red flags are present (see below), or if there is acute onset severe headache.

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### 4. Key Observations and Clinical Notes

- **Age**: 13 years, adolescent, common age for onset of primary headache disorders (migraine, tension-type).
- **Gender**: Male (slightly less common for migraine compared to females, but still possible).
- **History**: No relevant past medical history provided.
- **Symptoms**: Only "headache" reported; no details on duration, severity, frequency, associated symptoms (nausea, vomiting, photophobia, phonophobia, visual changes, fever, neck stiffness, trauma, etc.).
- **Clinical Note**: Further history and examination are essential to narrow the differential. Inquire about recent infections, trauma, family history of headaches, medication use, and psychosocial factors.

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### 5. Red Flags to Watch For

Immediate attention is required if any of the following are present:

- Sudden onset "thunderclap" headache (worst ever)
- Headache with fever, neck stiffness, photophobia (meningitis/encephalitis)
- Altered mental status, seizures, focal neurological deficits
- Papilledema or visual changes
- Headache worse with Valsalva or lying down (raised intracranial pressure)
- Recent head trauma
- Headache waking the patient from sleep or worse in the morning
- Immunosuppression or known malignancy

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**Summary:**  
Headache in a 13-year-old male is most commonly due to primary headache disorders, but secondary causes must be excluded, especially if red flags are present. A thorough history and physical examination are critical. If any red flags or abnormal findings are present, urgent neuroimaging and further workup are warranted.

**Recommendation:**  
Consult a healthcare professional for a comprehensive evaluation and management.