Hypokalemic
paraperesis unmasks Sj?gren’s disease

 

Ghosh
S, Mondal S, Chandra S K, Bandyopadhyay S

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Keywords:
Hypokalemia, Paraperesis, Distal Renal tubular acidosis, Sj?gren’s Syndrome

 

A 51 year old
female presented to the emergency department with complaint of both lower limb
progressive and painless weakness and inability to stand and walk for last 24
hours. She also mentioned that she had three episodes of vomiting but no loose
motion and fever. She was on treatment with beta-blockers and sulfonylurea for
hypertension and type-II diabetes mellitus. Review of her medical history was
not contributory to find any medications or previous or familial illness
leading to this flaccid paraperesis. Neurological examination revealed grade 1
and grade 2 power (MRC grading) in left and right lower extremities
respectively along with depressed deep tendon reflexes but no sensory signs and
autonomic dysfunction. Other physical examination findings including
ophthalmological examination were unremarkable.

 

At the time
of admission, her blood pressure was 150/80mmHg. Initial arterial blood gas
revealed hyperchloremic metabolic acidosis with normal anion gap and severe
hypokalemia. Routine electrocardiogram had presence of large ‘U’ waves. Blood
chemistry showed random sugar 180mg/dl, sodium 132 mmol/l, potassium 1.7
mmol/l, chloride 112mmol/l, bicarbonate 11mmol/l, creatinine 0.9 mg/dl, calcium
9.7 mg/dl, phosphorus 1.3 mg/dl and magnesium 1.4 mg/dl. Spot urinary potassium
was measured and found to be 24 mEq/l. Urine routine examination revealed
urinary pH of 7.0 but no cast and red blood cells. Electrolyte replacement was
started following which her clinical condition improved and there was no
residual weakness. Specific laboratory parameters including serum thyroid
stimulating hormone (1.5 uIU/ml), creatine kinase (248 U/L), vitamin B12 (564
pg/ml) and liver function test were found to be within normal limit.  A diagnosis of distal renal tubular acidosis
(dRTA) type-I was considered on the basis of hyperchloremic metabolic acidosis,
alkaline urinary pH, spot urinary potassium of 24 mEq/l and low plasma
bicarbonate. Ultrasound examination showed normal kidneys with no
nephrocalcinosis or stones. Autoimmune work up was sent in
order to find the cause of dRTA as autoimmune disorders including sjogrens’
syndrome, rheumatoid arthritis, systemic lupus erythematosus and autoimmune
hepatitis remained major secondary etiologies in the absence of other causative
medications. Though our patient denied to have any history of joint pain, rash
and classical sicca symptoms. Her antinuclear antibody (ANA) level was found to
be 4 positive in 1:100 dilution (fine granular pattern), RA factor and anti-CCP
were 27 IU/ml and 1.1 U/ml. Complete ANA profile by line blot assay showed 3
positive antibody titer to SS-A, SS-B and Ro-52.  Serum protein electrophoresis was normal.  A lip biopsy could not be done as they patient
didn’t give consent in the view of absence of any classical dry symptoms. Diagnosis
of primary SS was considered on the basis of nephrological involvement
presented as dRTA and positive auto-antibody results.

She was
treated with oral prednisolone on tapering dose starting with 40mg/day and
gradual tapering to a stable dose of 10mg/day. After one month of follow up her
serum bicarbonate was 24 mEq/l and potassium was 3.9 mEq/l.

 

 

Discussion:

Sj?gren’s
syndrome (SS), known to occur more in the 40–45 years age group
with a female predominance of 10:1, is a chronic autoimmune
inflammatory disease featuring both exocrine gland malfunction and extra-glandular
involvement. Most of the times, a diagnosis of  SS is only thought when symptoms like dry eye,
dry mouth are present in clinical practice. But there are handful of cases in
literature which show that even in the absence of classical sicca symptoms, a
diagnosis of SS is made. Extra-glandular involvement of SS includes skin,
joints, lung, heart, gastro-intestinal tract, thyroid, kidney, bladder and both
central and peripheral nervous system. Prevalence of renal involvement in SS
was found to be 2 to 67 percent in various studies. Interstitial nephritis is
the most common lesion reported in primary SS which may result in to latent or
overt tubular dysfunction. Clinical presentation can be distal renal tubular
acidosis, nephrocalcinosis, nephrogenic diabetes insipidus or even sometimes
proximal renal tubular acidosis or fanconi syndrome. Interstitial nephritis
most of the times occurs in conjunction with distal renal tubular acidosis but
dRTA can be present in some patients in spite of normal renal histopathological
findings. Exact mechanism of dRTA is not known till date but there are many
published articles featuring complete absence of the H-ATPase pump and anion
exchanger 1 (AE1) in the intercalated cells of the collecting tubules
that is largely responsible for distal proton secretion. High levels of
anticarbonic anhydrase antibodies affecting the functioning of carbonic
anhydrase in collecting ducts have been found in few occurrences.

 

Literature search revealed few
cases of flaccid hypokalemic quadriparesis secondary to distal renal tubular
acidosis unmasking the diagnosis of Sj?gren’s syndrome. But flaccid hypokalemic
paraperesis without sicca symptoms secondary to sj?gren’s syndrome is not
reported. Hypokalemic paraparesis is a rare entity in the
consideration of acute flaccid paraplegia.  A high index of clinical suspicion and methodical
approach are required in order to achieve the final diagnosis contributing to
hypokalemia. Missing the diagnosis can contribute to recurrent episodes of
hypokalemia and eventually respiratory arrest.

The frequency
of anti-Ro/SSA and anti-La/SSB antibodies has varied between studies, but
generally 60 to 80 percent of patients of primary SS exhibit one or both of
these auto-antibodies. ACR-EULAR sponsored classification criteria for SS has
given weighted score of 3 if these positive antibodies were found. But there
are no such literature featuring the sensitivity and specificity of these tests
for SS in the absence of classical sicca symptoms. Using the ACR-EULAR
classification criteria in the absence of dry symptoms  to diagnose SS would be inappropriate. This
criteria is materialized with the intent to be used in research trials of
emerging immunotherapy against SS.

 

 

 

Like our case,
a high index of suspicion and proper methodical approach is necessary to
diagnose the root cause of hypokalemic paralysis unmasking Sj?gren’s disease.

 

 

 

 

 

 

 

 

 

 

References:

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