Differential Diagnosis: Leonine Facies, Dementia, and Hyperactive Limbs in a 75-Year-Old with Prior Pulmonary TB
The most critical differential diagnosis to consider is lepromatous leprosy (Hansen's disease) with neurological complications, given the pathognomonic leonine facies combined with dementia and hyperkinetic movements. This presentation demands urgent evaluation for treatable infectious and inflammatory etiologies before attributing symptoms to primary neurodegenerative disease.
Primary Differential Diagnoses
1. Lepromatous Leprosy (Hansen's Disease) - MOST LIKELY
The leonine facies is virtually pathognomonic for lepromatous leprosy, characterized by:
- Thickened facial skin with deep furrows
- Loss of eyebrows (madarosis)
- Nasal collapse
- Nodular infiltration of facial tissues
Neurological manifestations include:
- Peripheral neuropathy affecting cognitive function
- Secondary CNS involvement (rare but documented)
- Movement disorders from nerve damage
- The history of pulmonary TB 8 years ago is relevant, as both are mycobacterial infections and may coexist
Critical action: Skin biopsy, slit-skin smear, and nerve biopsy are diagnostic. This is a treatable condition with multidrug therapy (rifampicin, dapsone, clofazimine).
2. Tuberculous Meningitis or CNS Tuberculosis
Given the history of pulmonary TB, reactivation or new CNS involvement must be excluded 1, 2:
- TB meningitis can present with dementia as the primary symptom 2
- May occur months after initial infection
- Hyperactive limbs could represent myoclonus or seizure activity
- Recent evidence shows TB survivors have 1.11-fold higher risk of Alzheimer disease and 1.48-fold higher risk of vascular dementia 3
- CNS TB specifically carries 1.76-fold higher dementia risk 3
Critical features to assess:
- Subacute onset over weeks to months
- Constitutional symptoms (fever, weight loss, night sweats)
- CSF analysis showing lymphocytic pleocytosis, elevated protein, low glucose
- Brain MRI showing basal meningeal enhancement, tuberculomas, or hydrocephalus
3. Corticobasal Syndrome (CBS)
The combination of dementia with hyperactive limbs fits CBS 4, 5, 4:
- Cortical sensorimotor dysfunction with limb apraxia
- Executive dysfunction and cognitive difficulties
- Asymmetric rigidity and other motor dysfunction
- Often caused by corticobasal degeneration (CBD), but sometimes AD, FTLD-PSP, FTLD-Pick's, or FTLD-TDP43 4
However, leonine facies is NOT a feature of CBS, making this less likely as the primary diagnosis.
4. Creutzfeldt-Jakob Disease (CJD)
Rapidly progressive dementia with movement disorders 6, 4:
- Myoclonus (which could appear as "hyperactive limbs")
- Cognitive decline over weeks to months
- Characteristic MRI findings (cortical ribboning, basal ganglia hyperintensity on DWI)
- EEG showing periodic sharp wave complexes
Leonine facies would NOT be explained by CJD, suggesting a separate or alternative diagnosis.
5. Dementia with Lewy Bodies (DLB)
Progressive cognitive-behavioral-Parkinsonism syndrome 4, 5:
- Fluctuating cognitive impairment
- Visual hallucinations
- Spontaneous extrapyramidal features
- REM sleep behavior disorder
The hyperactive limbs could represent:
- Myoclonus
- Tremor
- Restlessness
Again, leonine facies is unexplained, pointing away from pure DLB.
6. Mixed Etiology Dementia
In a 75-year-old, multiple pathologies are common 5:
- AD with vascular contributions (VCID)
- Post-TB cognitive impairment 3
- Medication effects
- Metabolic derangements
Diagnostic Algorithm
Step 1: Rule out treatable infectious/inflammatory causes
- Skin examination and biopsy for leprosy
- CSF analysis (cell count, protein, glucose, TB PCR, culture)
- Brain MRI with contrast
- Chest imaging to assess for active TB
- Syphilis serology (RPR/VDRL, FTA-ABS)
Step 2: If infectious workup negative, pursue neurodegenerative evaluation
- Detailed neurological examination for:
- Pattern of motor abnormalities (symmetric vs asymmetric)
- Type of hyperkinetic movements (myoclonus, chorea, tremor, dystonia)
- Cognitive domain assessment (memory, executive, language, visuospatial)
- Neuropsychological testing
- MRI brain with volumetric analysis
- EEG if myoclonus or rapid progression suggests CJD
Step 3: Syndromic classification 4, 5 Based on predominant cognitive domain:
- Amnestic syndrome: Consider AD, LATE, hippocampal sclerosis
- Dysexecutive/behavioral: Consider FTLD, AD with VCID
- Cognitive-motor syndrome: Consider CBS, PSP, DLB
Step 4: Consider biomarkers if diagnosis remains unclear
- CSF AD biomarkers (Aβ42, tau, p-tau)
- Amyloid or tau PET (if available and appropriate)
- DaTscan for suspected DLB
Critical Pitfalls to Avoid
- Do not assume primary neurodegenerative disease without excluding treatable causes - The leonine facies is a red flag for systemic disease
- Do not overlook TB reactivation - Elderly patients with prior TB have significantly elevated dementia risk and may develop CNS TB with atypical presentations 2, 3
- Do not dismiss the leonine facies as unrelated - This finding must be explained and suggests leprosy until proven otherwise
- Do not delay empiric treatment for TB meningitis if suspected - Mortality is high with delayed treatment 2
- Recognize that "hyperactive limbs" requires precise characterization - Myoclonus, chorea, tremor, and dystonia have different diagnostic implications
Most Likely Diagnosis
Given the triad of leonine facies (pathognomonic), dementia, and hyperactive limbs in a patient with prior mycobacterial infection, lepromatous leprosy with neurological complications is the primary diagnosis to pursue urgently. Concurrent or secondary neurodegenerative disease may coexist, particularly given the patient's age and TB history 3, but the leonine facies demands immediate dermatological and infectious disease evaluation.