A 32-year-old Pakistani man was admitted to the neurology department of a tertiary care hospital with a four-month history of numbness and severe tingling sensations in his hands and feet, which later progressed within 2 months to his forearms and legs in a glove and stocking manner. The patient also complained of unsteady gait due to loss of balance. He also complained of a rapid, painless diminution of vision in both eyes for 4 months. He was normotensive and non-diabetic with no history of smoking or alcohol intake and had normal bowel habits. On inquiry into his dietary pattern, he used to eat meat 2-3 times per week. Previously, he had no history of neuropathy, nephropathy, retinopathy, or macrovascular complications. He had no history of joint pain or any features favoring autoimmune disease, vasculitis, or thyroid-related disorders. He reported no recent exposure to chemicals. He belonged to a lower-middle socioeconomic family and none of his close family members suffered from such complaints. He was not taking any medications besides a linezolid-based regimen for MDR tuberculosis. He was diagnosed with pulmonary tuberculosis in December 2019 and classical first line ATT was initiated. Despite his good compliance and adherence to treatment, his clinical symptoms of tuberculosis infection worsened. The patient developed resistance to Isoniazid and Rifampicin after 4 months of classical first line ATT, which was confirmed by sputum for culture and drug sensitivity. After that, he was diagnosed with multidrug-resistant pulmonary tuberculosis, and a Linezolid-based regimen including Clofazimine, Bedaquiline, and Pyrazinamide was instituted. Linezolid was initiated orally at a dose of 600 mg. His sputum for AFB turned negative after 6 months of 2nd line antituberculosis drug treatment (Figure 1). The treatment regime was continued further as per WHO guidelines.
On general physical examination, the patient was afebrile with normal vital signs. An ophthalmological examination revealed a significant diminution of visual acuity in both eyes limited to hand motion, finger counting, and light perception. Contrast sensitivity and color perception were reduced in both eyes. However, the pupils were normal, equal in size, and they were reactive to light equally. Fundus evaluation revealed bilaterally symmetrically edematous discs. Neurological examination of the motor system revealed normal power (MRC scale) grade 4+/5 in all limbs proximally and distally. Sensations of pinprick, fine touch and proprioception were impaired in lower limbs up to the knee. His gate was a broad-based ataxic gait with a positive Romberg's sign. The remainder of the systemic examination was unremarkable.
A complete blood picture showed mild normocytic normochromic anemia. Liver enzymes, serum Urea and creatinine, serum electrolytes, thyroid profile, serum ferritin, serum vitamin B12, hemoglobin A1c, anti-neutrophilic antibody titers, and Serum protein electrophoresis levels were within the normal reference range. Cerebrospinal fluid analysis showed a minimal rise in protein (52 mg/dl) with normal CSF glucose and normal white blood cells and differential counts. The cerebrospinal fluid's opening pressure was 15 cm2H20. Nerve conduction studies showed a marked reduction in the amplitude of sensory nerves of the lower limbs compared to the upper limbs. Nerve conduction study findings were suggestive of length-dependent axonal sensory polyneuropathy (Table 1). Optical coherence tomography imaging of the optic nerve head revealed the increased thickness of retinal nerve fiber layers of 320 and 330 mum in the right and left eyes, respectively (normal 220+20 um). Fundoscopic images revealed bilateral optic disc edema (Figure 2). A visual field test performed by a visual field Analyzer revealed bilateral central scotoma Magnetic resonance imaging of the brain and optic nerve was unremarkable. Due to a lack of appropriate testing in Pakistan, the concentration of linezolid in the blood could not be determined.