What is true about tuberculoid leprosy and what are the next steps for a patient with a recent Mantoux test result increase and the absolute criteria for diagnosing neurocysticercosis?

Characteristics of Tuberculoid Leprosy and Management of TB and Neurocysticercosis

Tuberculoid Leprosy Characteristics

In tuberculoid leprosy, peripheral nerves are involved asymmetrically, which is a key diagnostic feature of this form of the disease. 1

Tuberculoid leprosy is characterized by:

• Asymmetrical peripheral nerve involvement with thickened, palpable nerves
• Strong cell-mediated immune response leading to granuloma formation
• Positive lepromin test (in approximately 40% of borderline-tuberculoid cases) 2
• Limited number of skin lesions (50% of borderline-tuberculoid patients present with a single skin lesion) 2
• Skin smears that are typically negative for acid-fast bacilli 3
• Nerve damage that occurs due to immune-mediated destruction of nerve fibers 1
• Destruction of cells harboring bacilli due to strong immune reaction 1

The clinical presentation differs significantly from lepromatous leprosy, which typically shows:

• Symmetrical nerve involvement in a pseudo-polyneuritic pattern
• Numerous skin lesions
• Negative lepromin test
• Easily detectable bacilli in skin and nerve cells 1

Management of TB Exposure

For a person with a Mantoux test conversion from 3mm to 10mm after 8 months following contact with an active TB patient:

A chest X-ray (CXR) should be the next step in management to rule out active tuberculosis before initiating preventive therapy. 4

Management algorithm:

1. Obtain CXR to rule out active TB
2. If CXR is normal (no evidence of active disease):
   • Proceed with isoniazid preventive therapy
   • The standard regimen would be isoniazid for 6-9 months (not 3 months as suggested in the options)
3. If CXR shows abnormalities suggestive of TB:
   • Further evaluation with sputum studies would be needed
   • Full treatment regimen would be required if active TB is confirmed

Repeating the Mantoux test is not indicated as conversion has already been documented.

Absolute Criteria for Neurocysticercosis Diagnosis

Direct visualization of the parasite on fundoscopy is an absolute criterion for the diagnosis of neurocysticercosis. 4

Important diagnostic considerations for neurocysticercosis:

• MRI is recommended for evaluation but is not itself an absolute diagnostic criterion 4
• Fundoscopic examination is essential before initiating anthelminthic therapy (strong recommendation, moderate evidence) 4
• Direct visualization of the parasite (scolex) provides definitive diagnosis 4
• CSF antibody testing by ELISA has limitations and is not considered an absolute diagnostic criterion 4

Clinical Pearls and Pitfalls

For Tuberculoid Leprosy:

• Nerve biopsy may be necessary for diagnosis in pure neuritic forms
• Sensory loss is an extremely common sequela that can lead to secondary trophic changes
• Treatment requires multidrug therapy with dapsone, rifampicin, and clofazimine 1
• Corticosteroids can reduce or prevent nerve damage during reversal reactions 5

For TB Management:

• A Mantoux conversion from <5mm to ≥10mm indicates recent infection
• Preventive therapy is indicated for recent converters regardless of age
• The 3-month isoniazid regimen mentioned in the options is inadequate; standard preventive therapy requires longer duration

For Neurocysticercosis:

• Fundoscopic examination must be performed before starting anthelminthic therapy to exclude intraocular cysticerci, as treatment could lead to blindness in these cases 4
• MRI with specialized sequences (FIESTA, 3D CISS, BFFE) provides enhanced resolution for detecting cysticerci in CSF spaces 4, 6
• Treatment approach varies based on the location and number of cysts 4