Likelihood of IIH in Atypical Patients
IIH can definitely occur in patients who are not obese women of childbearing age, but these "atypical" cases require more extensive investigation to exclude secondary causes of intracranial hypertension before confirming the diagnosis. 1
Defining Atypical IIH
The 2018 consensus guidelines explicitly define "atypical IIH" as patients who are not female, not of childbearing age, or who have a BMI below 30 kg/m². 1 This classification acknowledges that IIH exists outside the classic demographic but signals the need for heightened diagnostic vigilance.
Prevalence in Atypical Populations
While IIH predominantly affects obese women of childbearing age, the condition does occur in other populations:
- Pediatric cases represent approximately 49.6% of secondary intracranial hypertension cases in systematic reviews, demonstrating that age alone does not exclude the diagnosis. 2
- Among adult IIH cases, approximately 29.1% are male, indicating that while less common, men can develop this condition. 2
- Only 40.4% of all IIH cases (including secondary causes) are obese or overweight, meaning nearly 60% fall outside the typical weight profile. 2
Critical Diagnostic Imperative for Atypical Cases
Patients with atypical presentations require mandatory, in-depth investigation to ensure no underlying secondary causes are present. 1 This is not optional—the guidelines are explicit that atypical cases demand more rigorous workup.
Essential Investigations for Atypical IIH
The diagnostic algorithm remains the same but must be pursued more aggressively:
- Urgent MRI brain within 24 hours (or CT if MRI unavailable, followed by MRI when available) to exclude mass lesions, hydrocephalus, structural abnormalities, vascular lesions, and abnormal meningeal enhancement. 1, 3
- CT or MR venography is mandatory within 24 hours to exclude cerebral sinus thrombosis, which is particularly important in non-obese prepubertal children. 1, 3
- Lumbar puncture with opening pressure measurement following normal imaging, with CSF opening pressure ≥25 cm H₂O required for diagnosis. 1, 3
Secondary Causes to Exclude
Before diagnosing idiopathic IIH in atypical patients, systematically exclude:
- Anemia, particularly iron deficiency anemia, which is associated with IIH and may present with shorter disease course, pulsatile tinnitus, and transverse sinus stenosis. 4, 2
- Renal diseases and associated anemia. 4, 2
- Medications that can cause secondary intracranial hypertension. 2
- Infections causing secondary intracranial hypertension. 2
- Hormonal disorders inducing intracranial hypertension. 2
- Hypertension and recent weight gain. 2
Clinical Presentation Remains Similar
Regardless of demographic profile, the symptom complex remains consistent:
- Headache (present in 92% of cases) that is progressively more severe and frequent. 3, 5
- Transient visual obscurations (unilateral or bilateral darkening of vision lasting seconds). 3, 6
- Pulsatile tinnitus (pulse-synchronous whooshing sound). 3, 6
- Visual blurring and potential visual loss. 3, 6
- Horizontal diplopia from sixth nerve palsy. 3, 6
- Papilledema on examination (though IIH without papilledema is a rare subtype). 3, 7
Common Pitfall to Avoid
Even patients with typical IIH phenotype should be screened for secondary causes. 2 The most dangerous error is assuming that because a patient doesn't fit the typical demographic, IIH is unlikely—this can delay diagnosis and lead to permanent visual loss. Conversely, assuming IIH in an atypical patient without excluding secondary causes can miss treatable underlying conditions.
The recommendation is clear: obtain full blood counts and screen for secondary causes even when the presentation seems straightforward, particularly in patients with subacute onset. 4, 2
Prognosis in Atypical Cases
When secondary causes like anemia are identified and treated, patients may experience faster and better prognosis after appropriate treatment. 4 This underscores the importance of thorough investigation rather than defaulting to a diagnosis of idiopathic disease.