Clinical Analysis

Synthesis of Key Findings

Most Likely Diagnosis

Subacute Combined Degeneration (SCD) of the Spinal Cord secondary to Vitamin B12 (Cobalamin) Deficiency

• Posterior column signs dominate: impaired proprioception, positive Romberg, impaired fine touch - all classic for SCD. As Adams and Victor's states: "Loss of vibration sense is the most consistent sign... Position sense is usually impaired in parallel" (Adams and Victor's, Principles of Neurology, 12th Ed.)
• The asymmetric onset (left foot) progressing to bilateral involvement is typical - SCD is "roughly symmetrical and distal" but can begin asymmetrically
• The sensory level at the umbilicus (T10) could reflect the thoracic cord as the most affected segment - the textbook notes the MRI lesions "extend through the cervical and upper thoracic cords"
• Mild hyperreflexia (lateral column early involvement) with absent Babinski reflects early pyramidal involvement without full UMN syndrome - consistent with SCD
• Urinary retention is documented in SCD: "A small number of patients have symptoms of autonomic dysfunction, including urinary sphincteric symptoms"

• Chronic severe anemia (Hb 5-8 g/dL) - recurrent, treated but recurring - classic for megaloblastic anemia from B12 deficiency; current Hb of 15.1 is likely from recent transfusion/treatment
• MCV 95.4 fL - normal/high-normal; in a 16-year-old with iron-deficiency anemia from menorrhagia, the MCV would normally be low (microcytic). A normal MCV in this context may represent a "masking" of macrocytosis by concurrent iron deficiency (dimorphic picture), or recent treatment normalizing the index
• Hepatomegaly + elevated AST/ALT - B12 deficiency causes hepatic megaloblastosis and can cause transaminase elevation; hepatic involvement is well documented
• Low Free T3 (<1 ng/mL) with normal TSH and T4 - this is sick euthyroid syndrome (low T3 syndrome), commonly seen in systemic illness, malnutrition, and nutritional deficiency states; it does NOT indicate primary thyroid disease (TSH would be elevated in hypothyroidism)
• Frequent menses - menorrhagia is a common cause of iron deficiency, but chronic menorrhagia in an adolescent with malnutrition/malabsorption can precipitate combined B12 and iron deficiency
• Free fluid in pouch of Douglas - possible peritoneal manifestation; combined with hepatomegaly and neutrophilia, could suggest an underlying infection (schistosomiasis in an endemic region, see differential) contributing to nutritional deficiency
• Cystitis on ultrasound - in the context of urinary retention from neurogenic bladder, a secondary cystitis is expected

Differential Diagnoses

1. Neuroschistosomiasis (spinal schistosomiasis) - Important to consider in endemic regions (sub-Saharan Africa, Brazil)

• For: Hepatomegaly, free fluid in POD, possible endemic exposure, urinary retention (Schistosoma haematobium), progressive myelopathy
• Against: No eosinophilia mentioned, no fever, no previous urinary symptoms typical of S. haematobium (hematuria), RPR negative
• Schistosoma mansoni causes hepatic and spinal granulomas; Katayama fever includes hepatomegaly, free peritoneal fluid
• This remains a strong differential given the hepatomegaly + peritoneal free fluid + myelopathy combination, especially if the patient is from an endemic area

2. Compressive Myelopathy (e.g., spinal tumor, disc herniation, epidural abscess)

• For: Definite sensory level at T10, urinary retention, progressive bilateral weakness
• Against: No fever, no back pain mentioned, no history of trauma; the dorsal column-predominant picture with Romberg positivity and absent Babinski is more metabolic than compressive
• Must be excluded urgently with spinal MRI

3. Transverse Myelitis (inflammatory/autoimmune)

• For: Acute/subacute onset, sensory level, urinary retention, bilateral leg weakness
• Against: No fever, no preceding viral illness, no pain, 1-year sensory history argues against acute demyelination; pattern is more posterior column than complete transverse
• Could be related to NMO spectrum disorder (anti-AQP4) or MS

4. Vitamin E Deficiency Myelopathy

• For: Adolescent, spinocerebellar/posterior column degeneration, hepatomegaly (malabsorptive state)
• Against: No cerebellar signs, no family history, no fat malabsorption history documented
• The textbook describes this as mimicking SCD with posterior column + spinocerebellar involvement

5. Copper Deficiency Myelopathy

• For: Mimics SCD exactly (posterior and lateral column degeneration), can occur with malnutrition, elevated zinc can deplete copper
• Against: Rare; no gastric surgery or excessive zinc supplementation history

6. Multiple Sclerosis / Demyelinating Disease

• For: Young female, sensory level, posterior column involvement, Lhermitte may be present
• Against: No relapsing-remitting history prior, no optic neuritis, 1-year history suggests progressive not relapsing-remitting

7. Hereditary Spastic Paraplegia / Friedreich's Ataxia

• For: Young age, posterior column and pyramidal signs, progressive
• Against: No family history, acute-subacute onset rather than insidiously progressive, Friedreich's typically involves cerebellar signs and cardiomyopathy

Investigations

Urgent / Emergency

1. MRI Spine (whole spine, with gadolinium) - most urgent; rules out compressive lesion; in SCD will show T2 hyperintensity in posterior columns ("inverted V" sign on axial cuts); also detects transverse myelitis or epidural lesion
2. Urinary catheterization - relieve urinary retention immediately (bladder scan first to confirm retention)
3. Serum Vitamin B12 (cobalamin) level - expected <200 pg/mL (often <100 pg/mL in neurological disease)
4. Serum methylmalonic acid (MMA) - most sensitive marker of functional B12 deficiency; elevated even when serum B12 is borderline low
5. Serum homocysteine - elevated in B12 deficiency; also elevated in folate deficiency

Confirmatory / Etiological

1. Serum folate and RBC folate - distinguish from folate deficiency (which can also cause megaloblastic anemia but rarely causes myelopathy alone)
2. Peripheral blood smear - look for hypersegmented neutrophils (>5 lobes), macro-ovalocytes confirming megaloblastic anemia; may show dimorphic picture (iron + B12 deficiency)
3. Reticulocyte count, iron studies (serum iron, TIBC, ferritin) - iron deficiency from menorrhagia would lower MCV, masking macrocytosis
4. Anti-intrinsic factor antibodies - positive in ~60% of pernicious anemia (autoimmune gastritis); if positive, confirms pernicious anemia
5. Anti-parietal cell antibodies - positive in ~90% of pernicious anemia
6. Serum gastrin - elevated in achlorhydria associated with autoimmune gastritis/pernicious anemia
7. Copper and ceruloplasmin levels - to exclude copper deficiency myelopathy (important differential)
8. Vitamin E (alpha-tocopherol) level - especially if malabsorption suspected

For Schistosomiasis Differential (given hepatomegaly + POD free fluid)

1. Stool microscopy - Schistosoma mansoni eggs
2. Urine microscopy - S. haematobium eggs (terminal hematuria, urinary symptoms)
3. Serum schistosomal serology (ELISA) - antibodies to Schistosoma spp.
4. Full blood count differential - eosinophilia would strongly support helminthic infection
5. Abdominal USS - assess for periportal fibrosis (pipestem fibrosis of Symmers) characteristic of chronic hepatosplenic schistosomiasis

Neurological Workup

1. CSF analysis (after MRI confirms no mass/herniation) - usually normal in SCD; elevated protein or pleocytosis would suggest inflammatory/infectious myelopathy; oligoclonal bands for MS
2. Nerve conduction studies / EMG - may show sensory axonal neuropathy in advanced SCD
3. Somatosensory evoked potentials (SSEPs) - sensitive for posterior column dysfunction; typically delayed in SCD
4. Visual evoked potentials - subclinical optic involvement in B12 deficiency
5. Anti-AQP4 (NMO-IgG) and anti-MOG antibodies - if transverse myelitis suspected
6. Brain MRI - exclude intracranial demyelinating lesions (MS), B12 can also affect cerebral white matter

Additional

1. LFTs full panel, coagulation screen - hepatomegaly with elevated AST/ALT; assess for hepatic synthetic function
2. TSH, free T3, free T4 - already done; the low free T3 (<1 ng/mL) with normal TSH = sick euthyroid, no additional thyroid treatment needed
3. Urine culture - given cystitis on USS and urinary retention, rule out UTI (and Bilharzia cystitis if S. haematobium endemic)
4. Pelvic USS review - free fluid in POD; rule out ovarian pathology (follicular cyst rupture, pelvic inflammatory disease)

Treatment

Immediate Management

1. Urinary catheterization (indwelling Foley) - relieve retention, strict fluid balance, urine culture
2. Initiate Vitamin B12 replacement empirically - do NOT wait for confirmation if neurological involvement is present; early treatment is key to recovery

Vitamin B12 Replacement (SCD)

• Cyanocobalamin or Hydroxocobalamin 1000 mcg IM daily x 7 days (loading dose)
• Then 1000 mcg IM weekly x 4 weeks
• Then 1000 mcg IM monthly for life (if pernicious anemia or malabsorption is the cause)
• Hydroxocobalamin is preferred over cyanocobalamin in many centers (longer half-life, better tissue retention)
• If dietary deficiency (vegetarian/vegan): high-dose oral cyanocobalamin 1000-2000 mcg/day is effective for maintenance once stores replenished, but parenteral is preferred initially for neurological disease
• The textbook states: "The greatest improvements occur in patients whose disturbance of gait has been present for less than 3 months and recovery is usually complete if therapy is instituted within a few weeks after the onset of symptoms" - making early treatment essential

Address Underlying Cause

• If pernicious anemia (anti-IF antibodies positive): lifelong parenteral B12
• If nutritional: address diet, consider malabsorption workup (celiac serology, H. pylori)
• If menorrhagia-driven combined deficiency: gynecological management of menorrhagia (hormonal therapy, iron supplementation)

Iron Supplementation

• Given history of severe chronic anemia with frequent menses, concurrent iron deficiency is likely
• Ferrous sulfate 325 mg PO TID after meals, or IV iron if oral not tolerated
• Monitor reticulocyte response at 1 week (expected reticulocyte crisis at 5-10 days post-B12 replacement)

Folate

• Folic acid 5 mg PO daily - especially if megaloblastic anemia; IMPORTANT: never give folate alone without B12 in B12 deficiency, as it can precipitate/worsen neurological deterioration by correcting anemia while leaving cord disease untreated

If Schistosomiasis Confirmed

• Praziquantel 40 mg/kg in 2 divided doses (S. mansoni) or 60 mg/kg in 3 divided doses (S. haematobium)
• Corticosteroids may be added for spinal schistosomiasis (anti-inflammatory)

Neurological Supportive Care

• Physiotherapy - lower limb rehabilitation, gait training, proprioceptive exercises
• Bladder care - intermittent catheterization or indwelling catheter, monitor post-void residuals as cord function improves
• DVT prophylaxis - LMWH if significant motor involvement or immobility
• Analgesia for neuropathic symptoms if present (gabapentin, amitriptyline)

Monitoring

• Neurological examination weekly for first month
• Serum B12, MMA, homocysteine at 3 months to confirm correction
• Repeat MRI spine at 3-6 months to assess cord signal improvement
• Hematological response: reticulocyte rise at 5-10 days; Hb normalization by 6-8 weeks

A Note on the Thyroid Findings

Summary

• Adams and Victor's Principles of Neurology, 12th Ed. - Chapter on Vitamin B12 Deficiency (SCD), pp. 1176-1180
• Bradley and Daroff's Neurology in Clinical Practice - Metabolic and Hereditary Myelopathies, p. 776
• Recent review: Bernetti C et al. "A Comprehensive Overview of Subacute Combined Degeneration: MRI Diagnostic Challenges and Treatment Pathways." Brain Sci. 2025 [PMID: 41008332]
• Holroyd KB, Berkowitz AL. "Metabolic and Toxic Myelopathies." Continuum. 2024 [PMID: 38330479]